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THE   CYANIDE  HANDBOOK 


Published   by  the 

McGraw-Hill    Boole  Company 

" 


to  the  Bo  ok  Departments  of  the 

McGraw  Publishing  Company  Hill  Publishing-  Company 

Publishers  of  Books  for- 

Elec  trical  Worl  d  The  Engineering  and  Mining  Journal 

Engineering  Record  Power  and  The  Engineer 

Electric  Railway  Journal  American   Machinist 

Metallurgical  and  Chemical  Engineering 


THE 

Cyanide  Handbook 


BY 

J.  E.  CLENNELL,  B.Sc.  (LONDON) 

Associate  of  the  Institution  of  Mining  and  Metallurgy;    Associate 

of  the  Chemical,  Metallurgical  and  Mining  Society  of  South 

Africa;  Author  of  "Chemistry  of  Cyanide  Solutions," 

etc.;  Cyanide  Chemist  to  the  Creston-Colorada 

Company 


FIRST  EDITION  —  SECOND  IMPRESSION 
Corrected 


McGRAW-HILL    BOOK    COMPANY 
239  WEST  39TH  STREET,   NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.G. 

1910 


Copyright,  1910,    by  the   McGRAW-HiLL  BOOK  COMPANY 


GIFT  0% 

FRANK  H  rt«Q8E«t 


7%«  Plimpton  Press  Norwood  Mass.  U.S.A. 


INTRODUCTION 

NOTWITHSTANDING  the  fact  that  so  much  has  been  written 
about  the  cyanide  process  since  its  successful  establishment  in 
South  Africa  in  1890,  there  still  appear  to  be  some  aspects  of  the 
subject  which  are  orly  slightly  touched  upon,  or  quite  inadequately 
treated,  by  the  mi^iy  able  exponents  of  the  process,  and  many 
facts  of  great  value  to  the  practical  worker  can  only  be  gathered  by 
long  and  painful  search  through  technical  literature.  The  various 
mechanical  developments  of  the  process  have  been  dealt  with  by 
different  writers  too  numerous  to  mention,  and  books  have  been 
published  in  which  this  side  of  the  question  is  handled  in  a  fairly 
adequate  manner.  The  chemical  aspect  of  the  process  has,  how- 
ever, been  treated  only  in  a  fragmentary  and  imperfect  manner, 
although  valuable  contributions  to  our  knowledge  of  this  subject 
have  appeared  from  time  to  time,  chiefly  in  the  form  of  papers 
read  before  such  bodies  as  the  Chemical  and  Metallurgical  Society 
of  South  Africa,  the  Institution  of  Mining  and  Metallurgy,  and  the 
Society  of  Chemical  Industry. 

The  aim  of  the  present  work  is  to  bring  together  such  scattered 
information  in  a  handy  and  accessible  form,  which  will  appeal  to 
all  workers  interested  in  the  process,  whether  as  managers  of 
plants,  foremen,  chemists,  or  assayers.  Depending  as  it  does  on  the 
application  of  chemical  principles,  a  very  important  section  of  the 
work  connected  with  a  cyanide  plant  is  carried  on  in  the  labora- 
tory; this  department  will  therefore  receive  a  larger  share  of 
attention  than  is  usually  given  to  it  in  books  of  this  description. 

The  discussion  of  the  chemical  properties,  reactions,  methods 
of  manufacture,  and  analysis  of  cyanide  itself,  which  have  been 
scarcely  touched  upon  in  other  similar  books,  will  here  be  dealt  with 
in  sufficient  detail.  An  outline  will  be  given  of  the  latest  and  most 
approved  practice  in  modern  cyanide  plants,  but  without  going 
into  minute  details  of  working,  which  are  liable  to  constant  change. 


CONTENTS 

PAGE 

PART  I.     GENERAL 

INTRODUCTION v 

SECTION  I.     EARLY  HISTORY  OF  THE  CYANIDE  PROCESS      ....  3 

(A)  Discovery  of  Cyanogen  and  its  Chief  Compounds       ...  3 

(B)  Early  Observations  on  the  Solubility  of  the  Precious  Metals 

in  Cyanide 10 

(C)  Introduction  of  the   MacArthur-Forrest  Process     ....  24 
SECTION  II.     OUTLINE  OF  OPERATIONS  IN  THE  CYANIDE  PROCESS        .  33 

(A)  The  Dissolving  Process ' 33 

(B)  The  Precipitation  Process 38 

(C)  The  Smelting  Process 41 

PART  II.     CHEMISTRY 

SECTION  I.     CYANOGEN  AND  ITS  COMPOUNDS  WITH  NON-METALS  .      .  47 

(A)  Cyanogen 47 

(B)  Hydrocyanic  Acid 51 

(C)  Compounds  of  Cyanogen  with  Non-metals 56 

SECTION  II.     SIMPLE  METALLIC  CYANIDES 62 

Details  Respecting  Certain  Metallic  Cyanides 64 

Cyanides  of  Alkaline  Metals 65 

Cyanides  of  the  Alkaline  Earth  Metals 68 

Cyanides  and  Double  Cyanides  of  Zinc 69 

Cyanides  of  the  Iron  Group 71 

Cyanides  of  the  Precious  Metals 71 

Cyanides  of  Copper *    .  76 

Cyanides  of  Mercury 81 

Cyanides  of  Lead 83 

SECTION   III.      METALLIC    COMPOUNDS    OF     COMPLEX      CYANOGEN 

RADICALS 84 

(A)  Metallic  Compounds  of  the  Radical  RC6N6 84 

(B)  Metallic  Compounds  of  Radicals  in  which  Cyanogen  is  Com- 
bined with  Oxygen  or  a  Similar  Element 95 

SECTION  IV.     CHEMISTRY  OF  THE  DISSOLVING  PROCESS      ....  102 
SECTION    V.     CHEMISTRY    OF    THE    PRECIPITATION    AND    SMELTING 

PROCESSES 117 

SECTION  VI.     MANUFACTURE  OF  CYANIDE 127 

(A)  Production  of  Cyanides  from  Refuse  Animal  Matter     .      .  127 

vii 


viii  CONTENTS 

PAGE 

(B)  Production  of  Cyanides  from  Atmospheric  Nitrogen  .      .      .  128 

(C)  Production  of  Cyanides  from  Ammonia  or  Ammonium  Com- 
pounds       130 

PART  III.  PREPARATORY  TREATMENT  OF  ORE 
FOR  CYANIDING 

SECTION  I.     CRUSHING  MACHINERY 135 

(A)  Rock-Breakers 135 

(B)  Stamps 137 

SECTION  II.     GRINDING  MACHINERY 146 

(A)  Rolls 146 

(B)  Grinding  Mills 148 

(C)  Ball  Mills 152 

(D)  Tube  Mills 154 

SECTION  III.     MECHANICAL  HANDLING  OF    MATERIAL    FOR    CYANIDE 

TREATMENT 159 

(A)  Handling  of  Old  Accumulations 159 

(B)  Handling  of  Current  Mill-Product 165 

(C)  Transfer  of  Material  to  Higher  Levels 167 

(D)  Preparation  of  Ore  for  Direct  Cyanide  Treatment     .      .      .  170 
SECTION  IV.      HYDRAULIC  CLASSIFICATION,  SEPARATION,  AND  SETTLE- 
MENT OF  SLIMES 172 

(A)  Hydraulic  Classification  by  Means  of  Pointed  Boxes       .      .  172 

(B)  Separation  and  Settlement  of  Slimes 176 

SECTION  V.   AMALGAMATION  AND  CONCENTRATION 179 

(A)  Amalgamation  in  Relation  to  Cyanide  Treatment       .      .      .  179 

(B)  Concentration  in  Relation  to  Cyanide  Treatment       .      .      .  185 

PART  IV.    THE  DISSOLVING  PROCESS 

SECTION  I.     PERCOLATION 197 

(A)  Leaching  Vats 197 

(B)  The  Leaching  Process ' 200 

(C)  Double  Treatment 205 

(D)  Discharging  of  Treated  Material 206 

SECTION  II.    AGITATION 208 

(A)  Agitation  by  Mechanical  Stirrers 208 

(B)  Agitation  by  Circulating  the  Pulp  and  Injection  of  Air  .      .  210 

(C)  Andrew  F.  Crosse's  Slime  Treatment  Process 211 

(D)  Treatment  of  Slimes  by  Settlement  and  Decantation  .      .    .  212 
SECTION  III.     FILTRATION  BY  PRESSURE  AND  SUCTION 216 

(A)  Advantages  of  the  System 216 

(B)  Filter-Presses 216 

(C)  Filtration  by  Suction 221 

SECTION  IV.     HANDLING  OF  SOLUTIONS 235 

(A)  Sumps  and  Storage  Tanks 235 


CONTENTS  ix 

PAGE 

(B)  Settling  and  Clarifying  Tanks      ....      0      ....  236 

(C)  Pumps 237 

(D)  Piping  for  Conveying  Solutions 237 

(E)  Arrangements  for  Heating  Solutions 239 

PART  V.    THE  PRECIPITATION  AND  SMELTING  PROCESS 

SECTION  I.     ZINC-BOX  CONSTRUCTION  AND  PRACTICE 243 

(A)  Zinc-Box  Construction 243 

(B)  Circular  Vats  for  Zinc  Precipitation 245 

(C)  Cutting  and  Preparing  the  Zinc  Shavings 246 

(D)  Lead-Zinc  Couple 246 

(E)  Charging  the  Zinc  into  the  Boxes 247 

(F)  Conditions  which  Influence  Precipitation     .      .      .      .      ;      .  248 

(G)  Difficulties  in  Zinc  Precipitation 252 

(H)  Non-Accumulation  of  Zinc  in  Solutions 256 

(I)  Tests  for  Regulating  the  Working  of  the  Boxes     ....  256 

SECTION  II.     CLEAN-UP  OF  ZINC-BOXES 258 

(A)  Preliminary  Operations 258 

(B)  Separation  of  Precipitate  from  Coarse  Zino 258 

(C)  Removal  of  Precipitate  from  Box 259 

(D)  Settlement  and  Sifting  of  Precipitate 259 

SECTION  III.     ACID  TREATMENT  AND  ROASTING  OF  PRECIPITATE  .     .  261 

(A)  Acid  Treatment 261 

(B)  Roasting  of  Zinc-Gold  Precipitate 264 

SECTION  IV.     FLUXING,  SMELTING,  AND  REFINING  OF  THE  PRECIPI- 
TATE    266 

(A)  Fluxes  for  Zinc-Gold  Precipitate 266 

(B)  Mixing  of  Precipitate  and  Fluxes 267 

(C)  The  Fusion  Process p 268 

(D)  Use  of  Special  Fluxes ' 270 

(E)  Treatment  of  Matte 271 

(F)  Smelting  of  Zinc-Gold  Precipitate  with  Litharge    .      ...  272 

(G)  Nature  and  Properties  of  Cyanide  Bullion - .  274 

(H)  Refining  of  Bullion 275 

PART  VI.    SPECIAL  MODIFICATION  OF    THE 
CYANIDE    PROCESS 

SECTION      I.     DIRECT  TREATMENT  AFTER  DRY  OR  WET  CRUSHING     .  279 

SECTION    II.     CRUSHING  WITH  CYANIDE  SOLUTION 281 

SECTION  III.     ROASTING    BEFORE    CYANIDE    TREATMENT   ....  286 

Furnaces  with  Revolving  Rabbles 286 

Revolving  Cylindrical  Furnaces 288 

SECTION  IV.     USE  OF  AUXILIARY  DISSOLVING  AGENTS 293 

Oxidizers  in  Conjunction  with  Cyanide 293 

The  Bromocyanide  Process 295 


X  CONTENTS 

PAGE 

Bromocyanide  Practice  in  Western  Australia 295 

Use  of  Mercuric  Chloride 297 

SECTION  V.     ELECTROLYTIC  PRECIPITATION  PROCESSES 298 

The  Siemens-Halske  Process 298 

Later  Developments  of  Electrolytic  Process 300 

Electrolytic  Process  for  Gold-Copper  Ores 301 

Other  Electrolytic  Processes 303 

Solution  and  Electrolytic  Precipitation  in  the  same  Vessel     .      .  304 

SECTION    VI.     OTHER  PRECIPITATION  PROCESSES 306 

SECTION  VII.    TREATMENT  OF  CUPRIFEROUS  ORES 310 

PART  VII.    ASSAYING 

SECTION  I.     SAMPLING 317 

(A)  Sampling  of  Ores  and  Similar  Material  in  Bulk    .      .      .      .  317 

(B)  Sampling  of  Sand  and  Similar  Material 324 

SECTION  II.    ASSAY  OF  A  TYPICAL  SILICEOUS  ORE 333 

(A)  Crucible  Fire  Assay 333 

(B)  Cupellation  and  Parting 340 

SECTION  III.     SPECIAL  METHODS  OF  ASSAY    FOR    PARTICULAR    ORES 

AND  PRODUCTS 349 

(A)  The  Scorification  Assay 349 

(B)  Crucible  Fusions  for  Various  Classes  of  Ore 354 

Class         I.   Siliceous  Ores 355 

Class       II.   Basic  Ores 358 

Class      III.   Pyritic  Ores 359 

Class      IV.   Lead-Zinc  Ores 365 

Class        V.   Arsenical  Ores 365 

Class      VI.   Antimonial  Ores 366 

Class    VII.   Cupriferous  Ores 367 

Class  VIII.   Telluride  Ores 369 

(C)  Assay  of  Certain  Refractory  Materials 371 

SECTION  IV.     ASSAY  OF  GOLD  AND  SILVER  BULLION 378 

(A)  Fire  Assay  Method 378 

(B)  Volumetric  Methods 389 

PART  VIII.     ANALYTICAL  OPERATIONS 

SECTION  I.     ANALYSIS  OF  ORES  AND   SIMILAR  SILICEOUS   MATERIAL.  395 

Preliminary  Operations 395 

General  Outline  of  Analysis 396 

Estimation  of  Various  Ingredients 397 

SECTION  II.     ANALYSIS  OF  BULLION  AND  OTHER  MAINLY  METALLIC 

PRODUCTS 430 

Sampling  and  Preliminary  Operations 430 

Estimation  of  Precious  Metals 431 

Estimation  of  Base  Metals 433 

Non-Metals  and  Negative  Radicals 434 


CONTENTS  xi 

PAGE 

SECTION  III.    ANALYSIS  OF  CYANIDE  SOLUTIONS  AFTER  USE  IN  ORE 

TREATMENT 437 

Tests  used  in  Daily  Routine  of  Cyanide  Plant 438 

Estimation  of  Cyanogen  Compounds 440 

Estimation  of  Metals 442 

Estimation  of  Acid  Radicals  other  than  Cyanogen  Compounds    .  448 

Alkali  Determinations 451 

Organic  Matter 451 

Special  Tests 452 

SECTION  IV.    ANALYSIS  OF  COMMERCIAL  CYANIDE 455 

Sampling  and  Preparation 455 

Estimation  of  Acid  Radicals 456 

Estimation  of  Metallic  Radicals 459 

Moisture  and  Insoluble  Matter 461 

Calculation  of  Results 462 

SECTION  V.    ANALYSIS  OF  SUNDRY  MATERIALS 463 

(A)  Lime 463 

(B)  Coal 465 

(C)  Water 467 

PART  IX.     METALLURGICAL  TESTS 

SECTION      I.     DENSITY  DETERMINATIONS 477 

SECTION    II.     ALKALI  CONSUMPTION  TESTS 483 

SECTION  III.     SCREENING  AND  HYDRAULIC  SEPARATION      ....  485 

SECTION  IV.     CONCENTRATION  AND  AMALGAMATION  TESTS      .     .     .  487 

SECTION     V.     CYANIDE  EXTRACTION  AND  CONSUMPTION  TESTS     .      .  490 

Standard  Preliminary  Cyanide  Test 490 

Tests  to  determine  Conditions  of  Treatment 491 

Tabulation  of  Results 495 

SECTION  VI.    USEFUL  FORMULAE 496 

Conversion  of  Metric  Weights  and  Measures 498 

Atomic  Weights  (1909) 499 


PART  I 
GENERAL 


SECTION  I 

EARLY   HISTORY   OF   THE   CYANIDE   PROCESS 
(A)   DISCOVERY  OF  CYANOGEN  AND  ITS  CHIEF  COMPOUNDS 

Early  Use  of  Cyanogen  Compounds.  —  The  cyanide  process 
is  a  technical  application  of  certain  chemical  reactions  displayed 
by  a  group  of  substances  known  as  the  "  cyanogen  compounds." 
The  beginnings  of  its  history  must  therefore  be  traced  in  the 
beginnings  of  our  knowledge  of  those  compounds.  Mixtures  con- 
taining one  or  other  of  these  substances,  such  as  could  easily  be 
obtained  from  natural  sources,  have  probably  been  known  and 
used  from  very  ancient  times  without  any  accurate  knowledge  of 
their  composition.  Thus  it  is  stated  by  Hoefer1  that  prussic  acid 
was  known  to  the  ancient  Egyptians,  who  used  it  for  poisoning 
those  who  had  been  guilty  of  divulging  the  sacred  mysteries  of  the 
priests.  An  extract  of  laurel  leaves  seems  to  have  been  used  for 
similar  purposes  in  the  Middle  Ages. 

Discovery  of  Prussian  Blue.  —  In  1704  the  substance  now  known 
as  Prussian  blue  was  accidentally  discovered  by  Diesbach2  whilst 
endeavoring  to  prepare  a  red  coloring  matter  or  "  lake  "  by  mixing 
a  decoction  of  cochineal  with  alum,  green  vitriol,  and  fixed  alkali: 
Using  alkali,  which  had  previously  been  used  for  the  distillation  of 
animal  matter,  instead  of  a  red  precipitate,  he  obtained  a  fine  blue 
color.  The  discovery  was  communicated  to  Dippel,  who  improved 
and  simplified  the  process;  but  it  was  kept  secret  until  1724,  when 
Woodward3  published  a  method  of  making  Prussian  blue  by 
fusing  dried  blood  and  alkali,  and  treating  the  extract  with  alum, 
green  vitriol,  and  spirit  of  salt.  It  was  soon  found  that  other 
animal  matters  might  be  used  instead  of  blood,  and  many  chemists 

1  "Histoire  de  Chimie,"  I,  226. 

2  Macquer,   "  Dictionnaire  de  Chimie,"  I,  265.     See  also  "Miscellanea  Bero- 
linensis  ad  Incrementum  Scientiarum,"  I,  377  (1710). 

3  "Philosophical  Transactions,"  XXXIII,  15-24  (1724). 

3 


£  :  THE   CYANIDE   HANDBOOK 

occupied  themselves  with  the  preparation  and  examination  of  this 
remarkable  coloring  matter. 

Macquer's  Researches  on  Prussian  Blue.  —  The  first  attempt 
at  a  scientific  examination  of  it  appears  to  be  that  of  Macquer1 
(1752).  He  came  to  the  conclusion  that  it  consists  of  iron  charged 
with  an  excess  of  inflammable  matter  furnished  by  the  "  phlogisti- 
cated  alkali "  used  for  precipitating  it.  He  also  showed  that  the 
peculiar  principle  which  imparted  the  blue  color  might  be  removed 
from  Prussian  blue  and  transferred  to  an  alkali,  which  latter  thus 
lost  its  alkaline  properties  and  yielded  a  solution  from  which  pure 
Prussian  blue  could  be  obtained  again  by  addition  of  an  iron  salt 
and  an  acid.  He  had  thus  obtained  a  ferrocyanide. 

Prussic  Acid.  —  Other  investigators  followed,  notably  Berg- 
man and  Guyton,  the  latter  of  whom  gave  the  name  "  acide 
prussique"  to  the  substance  to  which  the  color  of  Prussian  blue 
was  supposed  to  be  due.  In  1782  important  researches  on  this 
substance  were  made  by  Scheele,2  who  succeeded  in  isolating 
prussic  acid  by  distilling  the  extract  (obtained  by  fusing  animal 
matter  and  alkali)  with  excess  of  sulphuric  acid;  he  showed  that 
pure  Prussian  blue  could  be  obtained  from  the  distillate  by  adding 
to  it  an  iron  salt  and  a  few  drops  of  sulphuric  acid.  He  concluded 
that  the  "coloring  material"  was  composed  of  aerial  acid  (i.e., 
carbonic  acid)  and  an  inflammable  substance.  He  also  showed 
that  the  neutral  salt  obtained  by  the  action  of  alkali  on  Prussian 
blue  (i.e.,  ferrocyanide  of  potassium  or  sodium)  is  a  triple  salt 
consisting  of  alkali,  a  little  iron,  and  the  coloring  material. 

Scheele' s  Observations  on  the  Cyanides  of  Gold  and  Silver.  — •  But 
the  most  interesting  observations  from  our  present  point  of  view 
are  those  which  he  made  on  the  cyanides  and  double  cyanides  of 
gold  and  silver,  and  attention  may  be  drawn  to  the  following 
remarkable  passages: 

"  The  calx  of  iron  is  not  the  only  one  which  has  the  property  of 
fixing  the  coloring  material,  but  this  also  happens  with  gold,  silver, 
copper,  and  perhaps  with  several  metallic  calces,  for  if  the  solutions 
of  the  same  are  precipitated  with  the  '  liquor  prsecipitans '  and  again 
dissolved  by  pouring  in  more  liquor,  the  solution  remains  clear  in 

1  "Memoire   de   1' Academic   des   Sciences":   see   Macquer's   "  Dictionnaire   de 
Chimie,"  I,  265-274  (1778). 

2  "Sammtliche   Physische  und   Chemische  Werke,"    II,   321-348   ("Versuche 
liber  die  Farbende  Materie  im  Berlinerblau"). 


EARLY  HISTORY  OF  THE  CYANIDE   PROCESS  5 

the  open  air,  and  the  calx  is  not  again  precipitated  by  the  aerial 
acid."  l 

Translated  into  modern  language  this  passage  means  that  when 
solutions  of  gold,  silver,  and  copper  salts  are  precipitated  by  a 
cyanide  solution  and  the  precipitate  redissolved  by  excess  of 
cyanide,  a  solution  is  formed  which  remains  clear  on  exposure  to 
air,  and  from  which  the  metallic  oxide  is  not  thrown  down  by 
carbonic  acid. 

"If  some  of  this  liquor"  (i.e.,  the  alkaline  extract  of  animal 
matter)  "be  dropped  into  a  completely  saturated  gold  solution, 
the  gold  is  thrown  down  as  a  white  precipitate,  but  if  much  of  the 
liquor  be  added,  it  is  again  dissolved.  This  solution  is  colorless 
like  water;  the  precipitate  is,  however,  insoluble  in  acids.  Silver 
is  thrown  down  white,  like  cheese;  if  more  liquor  be  added  the 
precipitate  is  again  dissolved."  2 

He  had  thus  prepared  the  double  cyanides  of  gold  and  silver, 
on  the  formation  of  which  the  extraction  of  the  precious  metals 
by  cyanide  entirely  depends. 

Berthollet  on  Composition  of  Prussic  Acid.  —  Berthollet3  (1787) 
repeated  and  extended  the  observations  of  Scheele,  showed  that 
the  views  previously  held,  that  ammonia  and  carbonic  acid  are 
contained  in  prussic  acid,  were  erroneous,  and  gave  the  correct 
composition  of  the  acid  as  follows:  "Hence  I  conclude  that 
hydrogen  and  nitrogen  exist  in  prussic  acid,  that  they  are  combined 
with  carbon,  and  that  when  oxygen  is  added  the  necessary  condi- 
tions for  forming  carbonate  of  ammonia  are  present."  He  was 
not  able,  to  determine  the  proportions  of  the  constituents,  however. 

Berthollet  also  seems  to  have  obtained  chloride  of  cyanogen, 
but  made  no  exact  investigation  of  it.  He  says  (loc.  cit.,  p.  35) : 
"If  oxygenated  muriatic  acid"  (i.e.,  chlorine)  "be  mixed  with 
prussic  acid  prepared  by  Scheele's  method,  the  former  is  converted 
into  muriatic  acid  and  the  latter  acquires  a  much  sharper  odor,  and 
appears  to  have  become  more  volatile:  its  affinity  for  alkalis  is 
still  further  diminished.  It  forms  no  Prussian  blue  with  iron 
solutions,  but  a  green  precipitate  which  becomes  blue  on  exposure 
to  light  or  mixture  with  sulphurous  acid." 

*IUd.,  p.  347. 
2  Ibid.,  p.  339. 

3"Annales  de  Chimie,"  I,  30  (1790):  "Extrait  d'un  M^moire  sur  1'Acida 
Prussique." 


6  THE  CYANIDE   HANDBOOK 

Artificial  Formation  of  Cyanides.  —  Clouet,1  in  1791,  published 
a  method  of  obtaining  cyanogen  compounds  which  is  the  basis  of 
many  methods  that  have  been  used  or  proposed  for  the  manufac- 
ture of  cyanide.  He  passed  ammonia  gas  through  a  porcelain  tube 
containing  charcoal  heated  to  redness,  and  received  the  issuing 
gases  in  vessels  containing  a  solution  of  ferrous  sulphate.  He 
found  that  the  product  exhibited  the  properties  recognized  by 
chemists  as  belonging  to  the  coloring  matter  of  Prussian  blue. 

Cyanides  in  Nature. — •  Vauquelin2  (1803)  showed  that  prussic 
acid  is  present  ready  formed  in  certain  vegetable  substances 
occurring  in  nature. 

Solubility  of  Gold  in  Cyanides.  —  Hagen,  in  1805  ("Unter- 
suchungen,"  I,  665),  is  reported  to  have  made  the  statement  that 
gold  is  dissolved,  not  only  by  free  chlorine  and  aqua  regia,  but  by  a 
solution  of  prussiate  of  potash.  I  have  not  been  able  to  confirm 
this  reference,  but,  if  correct,  it  would  seem  to  be  the  earliest  state- 
ment of  the  solubility  of  metallic  gold  in  cyanide  solutions.  The 
existence  of  a  soluble  "  prussiate  "  of  gold  was  of  course  well  known, 
having  been  discovered,  as  already  mentioned,  by  Scheele;  but  in 
all  references  to  this  substance  which  I  have  been  able  to  find  it  is 
formed  by  acting  on  salts  of  gold  and  not  on  the  metal  itself. 

Proust  on  Cyanides  and  F err o cyanides.  —  In  the  following  year 
(1806)  Proust  published  an  extensive  investigation  of  the  proper- 
ties of  the  prussiates,3  showed  that  iron  in  the  "  triple  prussiates  " 
(i.e.,  ferrocyanides)  exists  in  the  condition  of  the  "black  oxide" 
(i.e.,  in  the  ferrous  condition),  and  requires  the  addition  of  a  solu- 
tion of  the  red  oxide  (i.e.,  a  ferric  salt)  in  order  to  give  Prussian 
blue.  With  regard  to  the  reactions  of  cyanides  and  ferrocyanides 
with  gold,  he  remarks: 

t(  ~  ,,  (Triple  prussiate,        Nothing; 

[Simple       "  White  precipitate; 

which  becomes  a  fine  yellow.  On  heating  the  mixture,  the  pre- 
cipitate does  not  explode;  it  is  a  true  prussiate  of  gold.  Heated 
in  a  retort,  it  gives  water,  empyreumatic  oil  pretty  abundantly, 

1  "Annales  de  Chimie"  [1]  XI,  30-35:    "Memoire  sur  la  Composition  de  la 
Matiere  Colorante  du  Bleu  de  Prusse." 

2  "Annales  de  Chimie  et  de  Physique,"  XLV,  206. 

3  "Annales   de  Chimie,"   LX,  185-224,  225-252:    "Fails  pour  Servir  a  1'His- 
toire  des  Prussiates." 


EARLY  HISTORY  OF  THE  CYANIDE  PROCESS  7 

a  carbonaceous  gas  which  burns  with  a  blue  flame,  and  leaves 
a  residue  of  gold  mixed  with  charcoal  powder." 

Cyanogen  Obtained.  —  Proust  also  tried  the  effe'ct  of  heating 
cyanide  of  mercury,  and  found  that  it  gave  off  inflammable  matter 
which  burnt  with  a  red  and  blue  flame  with  a  yellowish  border. 
He  formed  the  erroneous  conclusion,  however,  that  the  gas  con- 
sisted of  a  mixture  of  prussic  acid  and  "gaseous  oxide." 

Researches  on  Prussic  Acid.  —  Further  researches  were  made  by 
Ittner1  (1809),  who  succeeded  in  obtaining  prussic  acid  by  the 
action  of  hydrochloric  acid  on  the  cyanide  of  mercury.  By  carry- 
ing out  this  process  and  condensing  the  distillate  in  a  mixture  of 
ice  and  salt,  Gay-Lussac,2  in  1811,  succeeded  in  obtaining  anhy- 
drous prussic  acid,  both  in  the  solid  and  liquid  form,  and  deter- 
mined its  boiling-point,  26.5°  C,  melting-point,  —  15°  C,  and 
specific  gravity,  .70583. 

Electrolysis  of  Ferrocyanides.  —  R.  Porrett,3  in  1814,  published 
a  paper  "  on  the  nature  of  the  salts  termed  triple  prussiates."  He 
electrolyzed  the  "triple  prussiate  of  soda"  (i.e.,  sodium  ferrocya- 
nide),  and  observed  that  ferrous  oxide  and  prussic  acid  are  obtained 
at  the  positive  pole  and  only  soda  at  the  negative  pole.  Hence  he 
concluded  that  the  iron  and  the  elements  of  prussic  acid  must 
together  constitute  a  peculiar  acid,  which  he  succeeded  in  isolating 
by  treating  a  solution  of  barium  ferrocyanide  with  the  exactly 
equivalent  quantity  of  sulphuric  acid.  He  also  discovered  (in 
1808)  the  acid  of  the  class  of  substances  now  known  as  "  thiocya- 
nates"  or  "sulphocyanides";  and  suggested  the  use  of  these  com- 
pounds for  the  quantitative  estimation  of  copper,  when  added 
together  with  a  reducing  agent. 

Gay-Lussac :  Analysis  of  Prussic  Acid  and  Cyanogen.  —  In 
1815  Gay-Lussac4  published  his  researches  on  prussic  acid,  in 
which  he  describes  the  analysis  of  prussic  acid  by  exploding  the 
vapor  with  oxygen  in  a  vessel  standing  over  mercury,  and  also  by 
passing  the  vapor  over  heated  iron.  He  determined  the  quantita- 
tive composition  of  mercuric  cyanide,  and  showed  that  the  gas 
produced  by  heating  this  compound  consists  only  of  carbon  and 

.# 

1  Ittner,  "Beitrage  sur  Geschichte  der  Blausaure." 

'Gay-Lussac,  "Note  sur  1'Acide  Prussique":  "  Annales  de  Chimie,"  LXXVII, 
128. 

a  Porrett,  "Philosophical  Transactions,"  XXVI,  527. 

4  Gay-Lussac,  "Recherches  sur  1'Acide  Prussique":  "Annales  de  Chimie," 
XCV,  156. 


8  THE  CYANIDE  HANDBOOK 

nitrogen,  in  the  proportion  (approximately)  of  6  parts  of  the  former 
to  7  of  the  latter.  He  proposed  the  name  "  Cyanogene  "  for  the 
new  gas,  and  having  shown  that  prussic  acid  is  a  compound  of 
equal  volumes  of  cyanogen  and  hydrogen,  he  suggested  for  it  the 
name  "acide  hydrocyanique." 

The  discovery  of  cyanogen  is  of  great  importance  in  the  history 
of  chemistry,  being  the  first  example  of  the  isolation  of  a  "  com- 
pound radical,"  that  is  to  say,  of  a  group  of  elements  associated 
together  and  acting  in  a  number  of  chemical  changes  as  though 
they  were  a  single  element. 

Davy's  Researches  on  Cyanogen.  —  The  observations  of  Gay- 
Lussac  were  confirmed  and  extended  by  Sir  H.  Davy,1  in  1816,  who 
electrolyzed  anhydrous  hydrocyanic  acid,  showed  that  no  water  is 
formed  by  the  combustion  of  cyanogen  in  oxygen,  and  also  decom- 
posed cyanogen  by  the  electric  spark,  and  found  that  carbon  was 
separated  and  a  volume  of  nitrogen  liberated  equal  to  that  of  the 
cyanogen  taken.  He  also  prepared  iodide  of  cyanogen  by  heating 
iodine  with  mercuric  cyanide. 

From  this  time  onward  many  chemists  occupied  themselves 
with  the  study  of  cyanogen  and  its  compounds,  and  we  can  here 
only  allude  to  a  few  of  the  more  important  discoveries. 

Cyanic  Acid.  —  In  1818,  Vauquelin  found  that  one  of  the 
products  obtained  when  cyanogen  gas  is  dissolved  in  water  is  an 
acid,  which  is  decomposed  by  stronger  acids  into  carbonic  acid  and 
an  ammonia  salt.  The  name  cyanic  acid  was  given  to  this  sub- 
stance; it  was  found  to  contain  cyanogen  and  oxygen,  and  gave 
salts,  known  as  cyanates,  containing  different  metals  in  combina- 
tion with  these  elements. 

Synthesis  of  Urea.  —  F.  Wohler2  noted  that  when  cyanogen  gas 
is  passed  into  solution  of  ammonia  various  bodies  are  formed, 
including  "  a  characteristic  crystalline  substance,  which,  however, 
does  not  appear  to  be  ammonium  cyanate."  In  1828 3  he  identified 
this  substance  as  urea,  and  showed  that  it  can  be  formed  by  direct 
transformation  of  ammonium  cyanate,  which  has  the  same  per- 
centage composition.  This  observation  is  very  interesting,  as 
being  the  first  example  of  the  formation  of  an  organic  body  from 

1  Davy,  "Gilb.  Ann.,"  LIV,  383.     "Journ.  of  Science  and  the  Arts,"  I,  288: 
"On  the  Prussic  Basis  and  Acid." 

2  Wohler,  "Pogg.  Ann.,"  Ill,   177  (1825). 
8  "Pogg.  Ann.,"  XII,  253. 


EARLY  HISTORY  OF  THE  CYANIDE   PROCESS  9 

purely  inorganic  materials,  for  it  had  already  been  shown  by 
Clouet  (1791)  that  cyanides  could  be  formed  from  ammonia  passed 
over  red-hot  carbon.  It  is  also  one  of  the  earliest  observed  exam- 
ples of  isomerism,  or  of  two  substances  having  identical  che'mical 
composition  but  different  properties,  the  reaction  being 
NH4-CNO  =  CO(NH2)2. 

In  1831,  J.  Pelouze1  showed  that  potassium  formate  is  one  of 
the  products  obtained  by  evaporating  an  aqueous  solution  of 
potassium  cyanide,  this  being  another  instance  of  the  artificial 
production  of  organic  compounds. 

Manufacture  of  Cyanides.  —  In  1834,  F.  and  E.  Rodgers2 
described  various  methods  of  manufacturing  cyanides,  including 
that  universally  practised  until  a  few  years  ago,  which  is  given  by 
them  in  the  following  terms:  "Cyanuret  of  potassium  may  be 
prepared  by  exposing  a  mixture  of  anhydrous  carbonate  of  potash 
and  anhydrous  ferrocyanuret  of  potassium  to  a  moderate  red  heat 
in  a  covered  crucible  for  about  20  minutes." 

Action  of  Acids  on  Ferrocyanides. —  In  1835,  Everitt3  gave  the 
correct  explanation  of  the  reaction  taking  place  when  potassium 
ferrocyanide  is  distilled  with  dilute  sulphuric  acid,  the  equation 
(expressed  in  modern  symbols)  being: 

3H2SO4  +  K4FeCy6  =  3KHSO4  +  KFeCy3  +  3HCy. 

obtaining  the  white  or  yellowish  insoluble  salt  (KFeCy3)  now  known 
as  Everitt's  salt. 

Haloid  Cyanogen  Compounds.  —  Bromide  of  cyanogen  was 
discovered  and  investigated  by  Serullas4  (1827),  who  also  studied 
and  determined  the  composition  of  the  analogous  chloride  of 
cyanogen  (first  observed  by  Berthollet:  see  above),  and  redis- 
covered and  investigated  the  iodide  of  cyanogen,  first  obtained  by 
Davy  (1816). 

Other  Investigators.  —  Further  important  researches  on  cyano- 
gen and  its  compounds  were  made  by  Liebig,  Bunsen,  Berzelius, 
Kuhlmann,  Berthelot,  Joannis,  Playfair,  and  many  others,  some 
of  which  will  be  referred  to  later  in  dealing  with  the  chemistry 

1  Pelouze,  "  Annales  de  Chimie  et  de  Physique,"  XLVIII,  395. 

2  Rodgers,    "Philosophical   Magazine,"    (3)    IV,    91:     "On   Certain    Metallic 
Cyanurets." 

3  Everitt,   "Philosophical  Magazine,"  (3)  VI,  97. 

*  Serullas,  "Annales  de  Chimie  et  de  Physique,"  (2)  XXVII,  184;  XXXV, 
291,  337;  XXXVIII,  370. 


10  THE  CYANIDE  HANDBOOK 

of  cyanide.  We  shall  now  proceed  to  describe  those  observations 
which  more  immediately  led  up  to  the  discovery  of  the  cyanide 
process. 

(B)    EARLY  OBSERVATIONS   ON   THE  SOLUBILITY  OF  THE 
PRECIOUS  METALS  IN  CYANIDE 

Elkingtoris  Patent.  —  The  earliest  definite  statement  of  the 
solubility  of  metallic  gold  and  silver  in  cyanide  solutions  appears 
to  be  that  contained  in  the  patent  taken  out  Sept.  25,  1840,  by 
J.  R.  and  H.  Elkington  (Brit,  patent,  No.  8447,  of  1840),  which 
was  based  on  information  supplied  to  them  by  Dr.  Alexander 
Wright,  of  Birmingham,  who  in  his  turn  appears  to  have  been  led  to 
the  discovery  by  the  observations  of  Scheele,  already  quoted.  The 
following  are  extracts  from  Elkington's  specification: 

"  We  take  oxide  of  gold  prepared  by  any  of  the  known  methods, 
or  metallic  gold  in  fine  division,  and  dissolve  the  same  in  a  solution 
of  prussiate  of  potash  or  soda;  to  about  two  ounces  of  gold  con- 
verted into  oxide  we  add  two  pounds  of  prussiate  of  potash  dis- 
solved in  one  gallon  of  water,  and  boil  the  same  for  half  an  hour; 
the  solution  is  then  ready  for  use."  .  .  ."We  claim,  therefore,  in 
respect  of  this  branch  of  our  invention,  the  method  of  coating, 
covering,  or  plating  the  metals  above  mentioned  with  gold  by  the 
use,  first,  of  an  oxide  of  gold  or  metallic  gold  in  fine  division  dis- 
solved in  prussiate  of  potash  or  any  soluble  prussiate,  and  also 
by  the  use  of  the  oxide  of  gold  dissolved  in  any  analogous  salt;  and 
secondly,  by  combining  the  action  of  a  galvanic  current,  with 
the  use  of  a  solution  of  gold  as  above  described,  giving  the  prefer- 
ence to  a  solution  of  gold  in  the  prussiate  of  potash  as  above  par- 
ticularly described." 

It  will  be  obvious,  from  the  quotations  already  given  from 
early  writers  (Proust,  Porrett,  and  others),  that  the  expression 
"  prussiate  of  potash "  signifies  the  cyanide  and  not  the  ferrocya- 
nide  of  potassium;  and  in  fact  it  appears  to  be  used  in  this  sense  as 
late  as  1880  (see  Clark's  specification,  U.  S.  Patent,  No.  229,586, 
quoted  below). 

Bagration:  Solubility  of  Gold  in  Cyanide.  —  In  1843,  Prince 
Pierre  Bagration l  published  his  paper  "  On  the  Property  which 
Potassium  Cyanide  and  Ferrocyanide  Possess  of  Dissolving 

1  Bagration,  "Bull,  de  I'Acad.  Imple  de  St.  Pet."  (1843),  II,  136.  See  ab- 
stract in  "Journ.  fur.  prakt.  Chem.,"  XXXI,  367  (1844). 


EARLY  HISTORY  OF  THE  CYANIDE   PROCESS  11 

Metals."  In  using  gold  plates  as  anodes  in  electro-gilding  opera- 
tions, he  had  observed  that  the  gold  continued  to  dissolve  in  the 
cyanide  solution,  even  when  the  electric  current  was  interrupted. 
He  therefore  tried  the  experiment  of  suspending  a  plate  of  gold  so 
as  to  be  partially  immersed  in  a  solution  of  potassium  cyanide,  and 
found  that  "  after  the  lapse  of  about  3  days  the  part  which  dipped 
into  the  liquid  was  almost  completely  dissolved.  The  strongest 
action  had  taken  place  in  the  upper  part  where  the  solution  and 
the  plate  were  in  contact  with  the  atmospheric  air."  He  found 
that  the  action  was  promoted  by  warming  the  solution,  and  that 
"  silver  and  copper  in  the  form  of  very  thin  plates  or  wires  likewise 
dissolve  "  [in  cyanide  solutions]. 

The  paper  concludes  as  follows:  "My  researches  lead  me  to 
suppose  that  hydrocyanic  acid  at  the  moment  of  formation  also 
possesses  this  property  [of  dissolving  gold];  but  it  is  certain  that 
in  future  cyanides  of  potassium  must  be  reckoned  among  the 
number  of  the  solvents  of  gold,  and  that  one  must  beware  of  using 
gold  or  silver  vessels  for  operations  which  require  the  use  of  these 
salts."  He  noticed  that  ferrocyanide  of  potassium  is  also  a  solvent, 
though  in  a  very  much  less  degree. 

Glassford  and  Napier  on  Gold  and  Silver  Cyanides.  —  In  1844, 
a  paper  was  published  by  C.  F.  O.  Glassford  and  J.  Napier,1 
"On  the  Cyanides  of  the  Metals  and  Their  Combinations  with 
Cyanide  of  Potassium,"  giving  considerable  information  about 
the  preparation  and  properties  of  the  cyanides  of  gold  and  silver, 
and  the  double  cyanides  which  these  form,  respectively,  with 
cyanide  of  potassium;  but,  strangely  enough,  the  solubility  of  the 
metals  without  the  aid  of  the  electric  current  is  not  referred  to, 
although  the  fact  is  mentioned  that  when  two  plates  of  gold  dipping 
in  cyanide  solution  are  connected  with  an  electric  battery,  the  gold 
dissolves  much  more  rapidly  from  one  plate  than  it  is  deposited  on 
the  other.  This  paper  contains  I  believe,  the  earliest  reference  to 
the  volumetric  method  of  estimating  cyanides  by  means  of  silver 
nitrate  solution,  now  universally  used  in  testing  cyanide  solutions 
(loc.  cit.,  p.  70). 

Eisner:  Influence  of  Oxygen  on  the  Solution  of  Metals  in 
Cyanide. — In  1846,  L.  Eisner,2  in  a  paper  called  "  Observations  on 

*  Glassford  and  Napier,  "Philosophical  Magazine,"   (3)  XXV,  56-71  (paper 
read  before  Chemical  Society,  Feb.  19  and  March  4,  1844). 
?  Eisner,  "Journ.  fur  prakt.  Chem.,"  XXXVII,  441, 


12  THE  CYANIDE  HANDBOOK 

the  Behavior  of  Reguline  Metals  in  an  Aqueous  Solution  of 
Potassium  Cyanide,"  showed  that  the  oxygen  of  the  air  played  an 
essential  part  in  the  solution  of  gold,  silver,  and  some  other  metals 
in  cyanide  solutions.  In  this  paper  he  remarks: 

"It  is  a  fact  known  for  some  years  past,  that  metallic  gold, 
silver,  copper,  iron  dissolve  in  aqueous  solutions  of  potassium 
cyanide,  even  without  the  assistance  of  the  galvanic  current,  at 
the  ordinary  temperature  of  the  air  (about  12-15°  C) "  .  .  .  "It  was 
very  probable  that  the  solution  of  the  last-named  metals  (Au,  Ag, 
Cd),  as  well  as  that  of  Cu,  Fe,  Zn,  and  Ni,  had  only  taken  place 
through  the  agency  of  oxygen,  so  that  if  this  supposition  were 
correct,  oxygen  must  have  been  removed  from  the  layer  of  atmos- 
pheric air  still  present  above  the  column  of  liquid." 

Eisner  describes  experiments  showing  that  the  amount  of 
oxygen  in  tubes  containing  gold  and  silver,  standing  over  cyanide 
solution,  was  gradually  reduced,  and  that  the  air  which  remained 
extinguished  a  lighted  match  when  the  latter  was  slowly  intro- 
duced. When  such  tubes  were  opened  under  water  or  mercury, 
these  liquids  rose  in  them  to  a  certain  height.  Mercury  gradually 
rose  in  a  tube  containing  cyanide,  silver,  and  air,  inverted  over  it. 
Finely  divided  metallic  silver  placed  in  a  well-stoppered  tube  filled 
with  cyanide  solution  showed  very  slight  action,  only  a  little  silver 
cyanide  being  obtained  on  acidulating  with  HC1;  but  after  filtering, 
the  liquid  passing  through  gave  a  considerable  precipitate  with 
this  acid,  showing  that  further  action  had  taken  place  on  exposure 
to  air. 

Eisner  formulated  no  equation  to  explain  the  combined  action 
of  cyanides  and  oxygen  on  gold  or  silver,  although  the  usually 
accepted  expression  of  this  reaction  goes  by  his  name.  He  classi- 
fies the  metals  according  to  their  action  on  cyanide,  as  follows: 

1.  Insoluble:  Pt,  Hg,  Sn. 

2.  Soluble  with  decomposition  of  water:  Fe,  Cu,  Zn,  Ni. 

3.  Soluble  with  aid  of  atmospheric  air,  without  decomposition 
of  water:  Au,  Ag,  Cd. 

Early  Cyanide  Extraction  Test.  — •  In  1849  there  appeared  an 
account  of  what  seems  to  have  been  an  early  attempt  to  utilize  the 
solubility  of  gold  in  cyanide  compounds  for  metallurgical  purposes. 
This  is  a  description  of  experiments  made  in  1848  by  Dr.  Duflos,1 
entitled,  "  Entgoldungsversuche  der  Reichensteiner  Arsenik- 

i  "Journ.  fur  prakt.  Chcm.,"  XL VIII,  C5-70  (1849). 


EARLY  HISTORY  OF  THE  CYANIDE   PROCESS  13 

abbrande."  In  consequence  of  the  statements  of  Bagration 
(quoted  above),  a  quantity  of  the  material  was  extracted  with  a 
very  dilute  solution  of  yellow  prussiate  of  potash.  The  liquid 
leaching  through  was  digested  with  hydrated  sulphide  of  iron  for 
the  purpose  of  converting  any  cyanide  of  gold  and  potassium  which 
might  be  present  into  sulphide  of  gold  and  ferrocyanide  of  potas- 
sium. The  residue  was  burnt,  after  washing  and  drying,  but  the 
ash  was  found  to  contain  no  gold.  Tests  made  with  a  mixture  of 
chloride  of  lime  solution  and  yellow  prussiate  gave  no  better 
result.  "  Liebig's  potassium  cyanide  was  not  tried,  not  so  much  on 
account  of  its  high  price,  as  because  the  considerable  amount  of 
ferrous  oxide  present  in  the  '  Abbrande,'  which  would  form  yellow 
prussiate  with  the  potassium  cyanide,  already  indicated  that  an 
unsatisfactory  result  was  to  be  expected  a  priori."  If  this  test 
had  not  been  omitted,  the  experimenter  might  very  possibly  have 
forestalled  Messrs.  Mac  Arthur  and  Forrest  by  nearly  40  years ! 

Faraday's  Researches  on  Gold  Leaf.  —  In  1856,  Faraday1 
delivered  a  lecture  before  the  Royal  Society  entitled,  "Experi- 
mental Relations  of  Gold  and  Other  Metals  to  Light,"  in  which 
he  showed  that  extremely  thin  films  of  gold,  capable  of  transmitting 
light,  could  be  produced  by  acting  upon  gold-leaf,  adhering  to  a 
plate  of  glass,  with  a  weak  solution  of  cyanide  of  potassium.  The 
method  of  obtaining  such  films  was  as  follows:  "If  a  clean  plate 
of  glass  be  breathed  upon  and  then  brought  carefully  upon  a  leaf 
of  gold,  the  latter  will  adhere  to  it;  if  distilled  water  be  immediately 
applied  to  the  edge  of  the  leaf,  it  will  pass  between  the  glass  and 
the  gold  and  the  latter  will  be  perfectly  stretched;  if  the  water  be 
then  drained  out,  the  gold-leaf  will  be  left  well  extended,  smooth, 
and  adhering  to  the  glass.  If,  after  the  water  is  poured  off,  a 
weak  solution  of  cyanide  be  introduced  beneath  the  gold,  the  latter 
will  gradually  become  thinner  and  thinner;  but  at  any  moment 
the  process  may  be  stopped,  the  cyanide  washed  away  by  water, 
and  the  attenuated  gold  film  left  on  the  glass." 

Faraday  also  emphasized  the  importance  of  air  in  this  reaction, 
and  gives  the  following  explanation  of  it  (loc.  cit.,  p.  147) : 

"  Air-voltaic  circles  are  formed  in  these  cases  and  the  gold  is 
dissolved  almost  exclusively  under  their  influence.  When  one 
piece  of  gold-leaf  was  placed  on  the  surface  of  a  solution  of  cyanide 
of  potassium,  and  another,  moistened  on  both  sides,  was  placed 

i  Faraday,   "Philosophical  Transactions,"  CXLVII,   145-181   (1857). 


14  THE  CYANIDE  HANDBOOK 

under  the  surface.,  both  dissolved;  but  twelve  minutes  sufficed  for 
the  solution  of  the  first,  whilst  above  twelve  hours  were  required 
for  the  submerged  piece.  In  weaker  solutions,  and  with  silver 
also,  the  same  results  were  obtained;  from  sixty  to  a  hundred-fold 
as  much  time  being  required  for  the  disappearance  of  the  sub- 
merged metal  as  for  that  which,  floating,  was  in  contact  both  with 
the  air  and  the  solvent." 

Again  (loc.  cit.,  p.  173):  "A  piece  of  ruby  paper"  (colored  by 
finely  divided  gold)  "  immersed  in  a  strong  solution  of  cyanide  of 
potassium  suffered  a  very  slow  action,  if  any,  and  remained  unal- 
tered in  color;  being  brought  out  into  the  air,  the  gold  very  gradu- 
ally dissolved,  becoming  first  blue." 

Use  of  Cyanide  in  Amalgamation.  —  The  extraction  of  gold  by 
means  of  mercury  had  long  been  known.  Rose1  states  that  it  has 
been  in  use  for  the  last  2000  years;  but  it  had  frequently  been 
observed  that  the  surface  of  the  mercury  became  coated  with  films 
of  various  nature,  which  impaired  its  effectiveness  for  amalgama- 
tion. It  was  found  that  these  films,  consisting  chiefly  of  grease  or 
of  oxides  and  carbonates  of  copper  and  other  base  metals,  could  be 
removed,  and  the  efficiency  of  the  mercury  restored,  by  treatment 
with  various  chemicals,  such  as  nitric  acid,  caustic  soda,  sal- 
ammoniac,  etc.  Among  others,  cyanide  of  potassium  was  found 
to  be  very  effective  for  this  purpose,  and  appears  to  have  been 
already  in  frequent  use  as  an  aid  to  amalgamation  in  America 
during  the  60's  of  the  last  century.  This  practice  was,  of  course, 
carried  out  in  ignorance  of  the  fact  that  cyanide  was  a  solvent  of 
gold,  and  thus  cannot  in  any  sense  be  considered  to  be  an  anticipa- 
tion of  the  cyanide  process.  One  or  two  writers,  however,  drew 
attention  to  the  solubility  of  gold  in  cyanide,  only  mentioning  the 
fact  as  a  drawback  to  its  use  as  an  aid  to  amalgamation.  Thus, 
Prof.  Henry  Wurtz,  in  a  memoir  read  to  the  American  Association 
for  the  Advancement  of  Science,  at  Buffalo,  Aug.  1,  1866,2  says: 
"  Early  in  my  investigations  I  found  that  no  supposition  of  ex- 
traneous films  or  coatings  of  air,  oxide  of  iron,  talc,  or  other  foreign 
matter  (though  undeniably  often  present  and  even  occasionally 
active  in  this  way),  was  available  in  the  general  explanation  of  the 
phenomena;  for  it  was  quickly  found  that  the  most  powerful 

1  "Metallurgy  of  Gold,"  4th  edition,  p.  91. 

2  See  "American  Journ.  of  Mining,"  JV  354  (Dec.  7,  1867):    "On  a  Theory 
of  ( fold  Genesis." 


EARLY  HISTORY   OF   THE  CYANIDE   PROCESS  15 

chemical  agents,  save  those  which  act  by  dissolving  and  removing  a 
superficial  film  of  the  gold  itself,  gave  no  aid  to  quicksilver." 
The  following  note  is  added: 

"  To  this  category  belongs  cyanide  of  potassium,  as  I  need  not 
inform  chemists.  Despite  the  highly  deleterious,  and  in  fact  dan- 
gerous, nature  (in  inexperienced  hands)  of  this  agent,  it  would  appear 
that  attempts  are  now  being  made  to  palm  it  off  upon  mining 
men,  especially  in  California,  as  a  new  and  highly  valuable  adjunct 
in  amalgamation.  As  a  writer  upon  this  subject,  I  feel  therefore 
called  upon  to  take  this  opportunity  to  say  that  many  experiments 
were  made  by  myself  three  or  four  years  since  with  the  cyanide,  in  the 
preliminary  amalgamation  of  copper  plates,  with  the  idea  that  it 
might  be  of  value,  in  connection  with  the  amalgam  of  sodium,  for  this 
purpose;  and  it  is  possible  that  it  might  be,  were  it  not  for  one  vital 
obstacle,  namely,  that  the  coating  thus  formed,  unlike  that  produced 
by  the  aid  of  sodium  alone,  tarnishes  with  great  readiness.  Alone, 
the  cyanide  is  very  feeble  in  its  action  in  this  way,  and  much  inferior  to 
nitric  acid,  the  common  agent  used.  I  find,  in  fact,  that  ammonia, 
mixed  with  sal-ammoniac  (indeed  almost  anything  which  will  dis- 
solve copper  or  its  oxides),  is  equally  available.  The  cyanide  has  been 
much  tested  in  Colorado,  but  mostly  abandoned.  The  new  project, 
apparently  started  in  California,  of  using  it  in  the  battery  and  the 
pan,  is  one  which  could  scarcely  interest  any  but  those  occupied 
in  the  vending  of  miners'  nostrums;  as  the  known  solubility  of  both 
gold  and  mercury  in  it  would  alone  be  fatal  in  the  view  of  an  expert. 
In  the  pan,  particularly,  another  destructive  agency  would  be  set 
up,  namely,  a  solvent  action  upon  the  sulphides  of  the  baser  metals, 
and  a  secondary  precipitation  of  the  latter  upon  the  quicksilver. 
The  subject,  however,  is  not  worth  the  space  that  would  be  required 
for  its  discussion  here." 

Rae's  Patent:  Cyanide  in  Conjunction  with  Electric  Current.  — • 
In  the  following  year  we  come  to  the  patent  of  Julio  H.  Rae  (U.  S. 
Patent,  No.  61,866;  Feb.  5,  1867)  for  an  "Improved  Mode  of 
Treating  Auriferous  and  Argentiferous  Ores."  This  is  the  first 
distinct  attempt  to  apply  cyanide  as  a  solvent  of  gold  in  ores, 
though  it  may  perhaps  be  questioned  whether  Rae  was  aware  of 
the  solubility  of  gold  in  cyanide  of  potassium  without  the  aid  of  an 
electric  current.  He  gives  a  figure  of  an  agitation  apparatus,  the 
object  being  to  dissolve  the  gold  and  silver,  and  precipitate  them 
again  on  a  cathode  of  copper  or  suitable  material.  The  process 
is  thus  described : 

"This  invention  consists  in  treating  auriferous  and  argentifer- 
ous ores  with  a  current  of  electricity  or  galvanism  for  the  purpose 
of  separating  the  precious  metals  from  the  gangue.  In  connection 
with  the  electric  current  suitable  liquids  or  chemical  preparations, 
such,  for  instance,  as  cyanide  of  potassium,  are  used,  in  such  a 
manner  that  by  the  combined  action  of  the  electricity  and  of  the 
chemicals,  the  metal  contained  in  the  ore  is  first  reduced  to  a  state 


16  THE  CYANIDE  HANDBOOK 

of  solution,  and  afterward  collected  and  deposited  in  a  pure  state, 
and  that  the  precious  metals  can  be  extracted  from  the  disinte- 
grated rock  or  ore  at  a  very  small  expense  and  with  little  trouble 
or  loss  of  time." 

The  agitation  apparatus  consisted  of  a  vertical  shaft,  to  which 
was  attached  a  metallic  cage,  the  bottom  of  the  shaft  resting  on  a 
plate  of  metal  (by  preference  platina)  at  the  bottom  of  a  jar  of 
glass  or  other  suitable  material.  The  shaft  was  to  be  connected 
with  the  positive  pole  of  a  battery,  so  that  shaft,  cage,  and  plate 
together  formed  the  anode,  while  the  other  pole  of  the  battery  was 
to  be  connected  with  a  thin  slip  or  coil  of  copper  or  suitable  material 
(suspended  in  the  liquid  above  the  ore)  and  "forming  a  base 
on  which  the  precious  metals  are  deposited.  By  the  action  of  the 
electric  current  the  action  of  the  chemicals  on  the  metals  con- 
tained in  the  rock  is  materially  facilitated  and  a  perfect  solution 
thereof  is  effected." 

The  use  of  the  expression  "  materially  facilitated  "  would  seem 
to  imply  that  Rae  supposed  cyanide  of  potassium  (the  only 
chemical  mentioned  in  the  specification)  would  have  some  action, 
even  without  the  electric  current. 

Cyanide  as  a  Solvent  of  Metallic  Sulphides.  —  The  use  of  cyanide 
of  potassium  as  a  solvent  in  the  treatment  of  ores  is  again  men- 
tioned in  1870  by  H.  C.  Hahn1  ("  Schwefel-metalle  gegen  Cyan- 
kalium"),  who  remarks  that  "Cyanide  of  potassium  is  not  only  a 
good  solvent  for  Ag,  Cu,  etc.  (Cl,  I,  Br,  O),  but  also  for  several 
sulphides;  thus,  CuS  (as  already  known),  AuS  and  AgS  dissolve 
easily;  ZnS  and  FeS  after  some  digestion  in  strong  cyanide 
solution."  He  also  notes  that  these  sulphides  dissolve  both  in 
the  pure  condition  and  in  ores.  He  describes  experiments  showing 
the  solubility  of  silver  sulphide  in  cyanide,  and  notes  that  the 
separation  of  silver  from  copper,  by  means  of  sulphureted  hydro- 
gen, from  solutions  in  which  the  metals  are  present  as  soluble 
double  cyanides,  is  imperfect,  owing  to  the  incomplete  precipita- 
tion of  the  silver  sulphide.  He  refers  to  the  application  of  cyanide 
in  ore  treatment  as  follows:  "With  regard  to  AuS,  I  will  mention 
that  its  solubility  in  KCy  has  already  found  practical  application. 
The  owner  of  the  Union  Mine  in  Amador  County,  California,  treats 
the  concentrates,  which  contain  200  to  6000  dollars  gold  per  ton, 
with  quicksilver  and  a  strong  solution  of  cyanide  of  potassium, 

iHahn,  "Berg-  und  Huttenm.  Zeit.,"  XXIX,  66  (Feb.  25,  1870). 


EARLY  HISTORY  OF  THE  CYANIDE   PROCESS  17 

and  extracts  23  per  cent,  more  of  the  total  gold  contents  than 
formerly  by  ordinary  amalgamation." 

Hahn  seems  to  have  ascribed  the  action  of  cyanide  to  the 
solubility  of  gold  sulphide  rather  than  of  metallic  gold;  and  it  is 
evident  also  that  the  practical  application  referred  to  was  one  in 
which  the  object  was  to  aid  amalgamation,  and  not  to  dissolve  the 
gold  in  cyanide. 

Skey  on  Relative  Solubility  of  Metals  in  Cyanide.  —  The  objec- 
tions to  the  use  of  cyanide  as  an  aid  to  amalgamation  are  again 
referred  to  by  W.  Skey,1  in  an  article,  read  Jan.  29,  1876,  "On  the 
Electromotive  Order  of  Certain  Metals  in  Cyanide  of  Potassium, 
with  Reference  to  the  Use  of  this  Salt  in  Milling  Gold."  He  noted 
that  cyanide  had  been  used  with  marked  effect  in  preventing  the 
"  flouring  "  of  mercury  during  the  treatment  of  blanketings  at  the 
Thames  Gold-Field,  New  Zealand,  and  ascribes  the  action  to  the 
solvent  effect  of  cyanide  on  a  film  of  mercurial  salts  produced  by 
the  action  of  soluble  ferric  salts,  which  "either  oxidize  or  chloro- 
dize  the  surface  of  any  mercury  which  they  may  be  in  contact 
with." 

To  produce  this  effect,  the  cyanide  must  dissolve  a  portion  of 
the  mercury.  "  Moreover,  in  thus  contemplating  the  contingencies 
entailed  or  risked  by  the  use  of  any  alkaline  cyanide  in  such  milling 
operations,  it  must  be  remembered  that  both  gold  and  silver  are 
not  absolutely  insoluble  in  these  cyanides.  Now  the  loss  of  mer- 
cury in  this  way  may  not  be  serious,  but  if  gold  or  even  silver 
be  thus  lost  (that  is,  by  its  solution),  even  in  much  less  quantity 
than  mercury  well  could  be,  the  loss  then  may  be  serious.  Whether 
the  loss  of  metal  certain  to  be  entailed  by  the  use  of  cyanide  of 
potassium  falls  upon  the  mercury,  or  upon  the  gold  or  silver  of 
these  blanketings,  conjointly  or  separately,  depends  entirely  upon 
this  relative  affinity  of  these  metals  for  this  salt,  or  in  other  words 
it  depends  upon  their  electromotive  order  therein."  He  shows  the 
commonly  accepted  view,  that  mercury  is  positive  to  gold  and 
silver  in  cyanide  solutions,  to  be  erroneous,  and  that  mercury  is  in 
reality  very  decidedly  negative;  thus,  metallic  gold  in  contact 
with  a  solution  of  mercuric  cyanide  would  rapidly  dissolve 
and  mercury  be  reduced.  He  gives  the  following  as  the  elec- 
tromotive order  of  metals  in  potassic  cyanide,  from  negative  to 
positive : 

i  Skey,  "Trans.  Proc.  N.  Z.  Inst./   VIII,  334-337. 


18  THE  CYANIDE   HANDBOOK 

—  Carbon  Lead 

Platinum  Gold 

Iron  Silver 

Arsenic  Tin 

Antimony  Copper 

Mercury  +  Zinc. 

"  Most,  if  not  all,  the  sulphides  or  other  ores  occurring  in  nature 
are  negative  to  the  whole  series.  Any  of  these  metals  will  generally 
precipitate  the  ones  named  above  it  from  its  cyanide  solution"; 
thus,  gold  precipitates,  mercury  and  silver  gold,  taking  its  place 
in  the  liquid.  "  Thus,  it  appears,  a  loss  of  gold  by  solution  of  it 
must  frequently  happen  whenever  cyanide  of  potassium  is  em- 
ployed to  assist  in  the  amalgamation  of  blanketings,  or  other 
auriferous  stuff.  In  fact,  all  that  loss  of  metal  occasioned  by  its 
solution,  and  most  of  which  is,  as  we  have  seen,  a  necessity  in- 
volved in  the  working  of  the  process  itself,  falls  upon  the  gold  and 
silver  present,  the  mercury  being  positively  protected  from  the 
action  of  this  salt  by  these  more  valuable  metals."  They  also 
think  the  loss  would  be  greater  if  the  operation  were  conducted 
in  iron  pans,  and  also  greater  with  a  strong  cyanide  solution  than  a 
weak  one,  and  suggests  a  method  of  minimizing  the  loss  by  passing 
the  waste  liquor  in  a  thin  stream  over  copper  plates  (presumably 
with  a  view  to  precipitating  the  dissolved  gold  and  silver). 

Dixon  on  Treatment  of  Pyritic  Ores  with  Cyanogen  Compounds 
and  Oxidizers.  —  In  1877,  W.  A.  Dixon1  published  a  paper  "  On 
a  Method  of  Extracting  Gold,  Silver  and  Other  Metals  from 
pyrites,"  which  was  read  before  the  Royal  Society  of  New  South 
Wales,  Aug  1,  1877.  After  giving  an  account  of  various  methods 
tried  for  the  treatment  of  ores  containing  sulphides  of  Cu,  Pb,  Sb, 
Fe,  As,  etc.,  and  rich  in  gold  and  silver,  and  noting  that  amalga- 
mation and  chlorination  gave  unsatisfactory  results,  he  describes 
a  number  of  experiments  made  with  cyanides  and  ferrocyanides 
as  solvents,  both  alone  and  in  conjunction  with  various  oxidizing 
agents.  With  regard  to  cyanide,  he  says : 

"  Prince  Bagration  and  Eisner  [Watt's  "  Diet " :  "  Cyanides  of 
Gold  "]  have  observed  that  precipitated  gold  is  soluble  in  cyanide 
of  potassium  if  exposed  to  the  air;  and  the  latter  says  also  in  ferro- 
cyanide  of  potassium.  A  patent  was  applied  for  in  America  in  1868 

i  Dixon,  "Proc.  Royal  Soc.  N.  S.  W,"  XI,  93-111. 


EARLY  HISTORY  OF  THE  CYANIDE  PROCESS  19 

for  the  use  of  cyanide  of  potassium  for  the  extraction  of  gold  from 
its  ores,  but  I  have  no  particulars  of  the  process."  (This  possibly 
refers  to  Rae's  patent,  mentioned  above.)*  "  It  seemed  to  me,  how- 
ever, that  the  high  price  of  this  salt,  its  instability  when  exposed  to 
the  air  and  in  solution,  and  its  extremely  poisonous  properties, 
precluded  its  use  for  this  purpose.  On  trying  the  reaction  between 
precipitated  gold  and  cyanide  of  potassium,  I  found  that  it  was 
extremely  slow  if  the  gold  was  at  all  dense.  In  presence  of  alkaline 
oxidizing  agents,  however,  I  found  that  the  solution  of  gold  was 
sufficiently  rapid.  Thus,  on  standing  overnight,  the  quantity  of 
gold  and  cyanide  of  potassium  solutions  being  similar  in  each  case, 
with  the  cyanide  alone,  traces  only  of  gold  were  dissolved,  but  with 
the  addition  of  calcium  hypochlorite,  ferrocyanide  (ferricyanide?) 
of  potassium,  or  binoxide  of  manganese,  all  the  gold  was  dissolved; 
with  chromate  of  potassium,  a  small  quantity;  with  permanganate 
of  potassium,  none.  With  ferrocyanide  of  potassium  alone  I  did 
not  obtain  any  gold  in  solution  after  standing  some  days,  but  I 
thought  that  with  suitable  oxidizing  agents  it  might  be  obtained  in 
solution  according  to  the  equation 

4Au  +  2K4FeCy6  +  7O  +  4H2O  =  4AuCy3  +  Fe2O3  +  8KHO. 

In  the  cold,  however,  with  the  exception  of  ferricyanide  of 
potassium,  none  of  the  above  oxidizing  agents  had  any  effect,  but 
heated  to  212°  F.,  the  reaction  with  all  of  them  was  sufficiently 
rapid,  and  I  found  that  this  was  also  the  case  with  permanganate." 

Precipitation  on  Silver  and  Copper.  —  For  precipitation,  he 
suggests  first  filtering  the  hot  solution  through  finely  divided  metal- 
lic silver  to  recover  the  gold,  and  then  precipitating  the  silver  as 
sulphide;  he  found,  however,  "  that  copper  in  any  form  precipitated 
both  gold  and  silver  from  the  solution,  or  at  all  events  that  these 
metals  (i.e.,  gold  and  silver)  were  not  dissolved  until  the  copper 
had  all  gone  into  solution;  also,  that  if  the  copper  was  present  as 
sulphide,  the  silver  was  transformed  into  sulphide,  which  is  insolu- 
ble." 

To  remove  dissolved  copper,  he  suggests  digesting  the  alkaline 
solution  with  ferrous  hydrate,  which  would  at  the  same  time  con- 
vert any  cyanide  present  into  ferrocyanide,  "  which  has  the  impor- 
tant advantages  of  being  exceedingly  stable  and  non-poisonous." 

Extraction  Tests  on  Ores.  —  Various  experiments  are  then 
detailed,  on  roasted  arsenical  pyrites,  and  other  pyritic  ores,  using 


20  THE  CYANIDE  HANDBOOK 

mixtures  of  ferrocyanide  with  different  oxidizers  in  hot  solutions, 
"  A  portion  of  roasted  arsenical  pyrites  was  digested  at  212°  for 
twelve  hours  with  \  oz.  ferrocyanide  of  potassium,  32  gr.  oxide  of 
manganese  (20  Ib.  per  ton),  and  sufficient  water,  made  alkaline 
with  soda,  to  make  a  cream:  the  solution  yielded  9  oz.,  8  dwt., 
19  gr.  gold  per  ton,  leaving  1  oz.,  9  dwt.,  15  gr.  This  was  the  best 
result  obtained  with  this  pyrites,  the  yield  with  other  oxidizing 
agents  and  by  more  prolonged  digestion  being  all  somewhat  lower." 
In  another  case  the  material  was  previously  roasted  with  salt, 
and  extracted  with  acid  to  remove  copper.  The  material  then 

contained 

Gold,    8  oz.,    Odwt.,  19  gr.; 
Silver,  49    "    11     "         5    " 

and  yielded  from  3  oz.  12  dwt.  to  5  oz.  1  dwt.  of  gold  and  from 
46  oz.  to  46  oz.  3  dwt.  of  silver  per  ton.  "  This  showed  that  all  the 
silver  which  had  been  converted  into  chloride  during  the  roasting 
was  obtained  in  solution  as  cyanide.  With  the  gold,  on  the  other 
hand,  all  the  results  showed  that  with  complex  pyrites  a  portion 
only  could  be  obtained  in  solution,  either  in  mercury  or  in  water  as 
cyanide  or  chloride,  whilst  none  could  be  obtained  as  sulphide.77 
These  results  did  not  appear  to  Dixon  to  be  sufficiently  satisfac- 
tory to  warrant  further  investigation,  and  the  remainder  of  the 
article  is  devoted  to  the  discussion  of  smelting  processes,  etc.  It 
would  seem,  however,  that  additional  tests  on  the  lines  of  the  exper- 
iments detailed  might  probably  have  led  to  the  discovery  of  a 
workable  cyanide  process. 

Solubility  of  Silver  in  Cyanide.  —  Some  interesting  remarks 
on  the  solubility  of  silver  in  cyanide  solutions  are  to  be  found  in 
Percy's  "  Metallurgy  " 1  (published  in  1880),  although  the  explana- 
tion he  gives  of  the  reaction  would  seem  to  be  quite  erroneous. 
He  states  that  "  metallic  silver  dissolves  in  a  hot  aqueous  solution 
of  cyanide  of  potassium,  but  slowly  and  sparingly,  as  shown  by  the 
following  experiment  by  R.  Smith.  A  single  silver  leaf  was  heated 
during  several  hours  in  a  concentrated  aqueous  solution  of  cyanide 
of  potassium,  and  it  was  found  that  only  a  small  quantity  of  silver 
had  been  dissolved.  Christomanos,  on  the  other  hand,  asserts 
that  pure  silver  dissolves  readily  in  a  hot  solution  of  this 'salt 
(Fresenius,  Zeit.  fiir  Anal.  Chem.,  VII,  301;  1868).  In  this  case, 
hydrogen  must  be  evolved  according  to  the  following  equation, 

1  J.  Percy,  "Metallurgy:    Silver  and  Gold,"  Part  I,  p.  115. 


EARLY  HISTORY  OF  THE  CYANIDE  PROCESS  21 

unless  the  silver  is  oxidized  by  oxygen  derived  from  any  cyanate  of 
potash  that  might  be  present;  though  in  the  experiment  by  R. 
Smith,  above  recorded,  no  evolution  of  hydrogen  was  observed: 

4KCy  +  2Ag  +  H2O  =  2KCyAgCy  +  K2O  +  2H." 

Cyanide  as  an  Aid  to  Amalgamation.  —  In  1880-81  three  patents 
were  taken  out  in  the  United  States,  all  of  them  involving  the  use 
of  cyanide  or  some  cyanogen  compound  in  ore  treatment;  but  the 
chemical  being  added  not  as  a  solvent  but  as  an  aid  to  amalgama- 
tion, these  processes  have  no  direct  bearing  on  our  subject,  though 
they  are  of  some  interest  as  showing  the  state  of  metallurgical 
knowledge  at  the  time,  shortly  before  the  introduction  of  the  cya- 
nide process.  So  far  from  utilizing  the  solvent  action  of  cyanide, 
the  latter  would  be  actually  a  drawback  in  any  attempted  practical 
application  of  these  patents.  The  specifications  referred  to  are: 

(1)  U.  S.  patent,  No.  229,586:  Thos.  C.  Clark: 
Filed  Dec.  27,  1879;  issued  July  6,  1880: 

"Extracting  Precious  Metals  from  Ores." 

(2)  U.  S.  patent,  No.  236,424:  Hiram  W.  Faucett: 
Filed  July  13,  1880;  issued  Jan.  11,  1881: 

"Process  of  Treating  Ore." 

(3)  U.  S.  patent,  No.  244,080:  John  F.  Sanders: 
Filed  April  16,  1881;  issued  July  12,  1881: 

"Composition  for  Dissolving  the  Coating  of  Gold  in  Ore." 

Clark's  Process.  —  In  Clark's  process  the  ore  is  roasted  and 
thrown  while  hot  into  a  bath  formed  of  a  solution  of  salt,  prussiate 
of  potash,  and  caustic  soda  or  caustic  potash,  the  object  being 
to  effect  desulphurization  and  disintegration,  so  as  to  bring  the 
precious  metals  into  a  suitable  form  for  amalgamation  by  freeing 
them  from  the  union  and  influence  of  baser  metals. 

Faucett  Process.  —  In  Faucett's  process  the  crushed  ore  is  to 
be  heated  and  subjected,  under  pressure,  to  the  action  of  "  disinte- 
grating chemicals  "  in  solution  in  a  closed  vessel,  after  which  it  is  to 
be  further  pulverized  and  amalgamated.  The  pressure  is  effected 
by  the  steam  generated  by  contact  of  the  hot  ore  with  the  chemical 
solution.  The  chemicals  contained  in  the  solution  are  chloride  of 
sodium,  nitrate  of  potash,  cyanide  of  sodium,  sulphate  of  protoxide 
of  iron,  and  sulphate  of  copper,  with  or  without  admixture  of 
hydrofluoric  acid,  fluoride  of  potassium,  or  fluoride  of  sodium. 

Sanders'  Process.  —  In  Sanders'  process,  a  mixture  of  cyanide 
of  potassium  and  phosphoric  acid  is  used  to  remove  "  the  coatings 


22  .         THE  CYANIDE  HANDBOOK 

that  envelop  gold  in  the  ore  and  that  consist  usually  of  various 
metallic  oxides  and  of  silver. "  .  .  .  "  After  agitation  the  mixture 
above  mentioned  will  be  found  "  to  have  dissolved  the  oxides  and 
the  sulphurous  coatings  of  the  ore,  and  the  agitation  of  the  barrel 
or  vessel  removes  the  dissolved  impurities,  leaving  the  gold  free 
and  exposed,  and  permitting  it  to  be  amalgamated  by  the  addition 
of  quicksilver  in  the  usual  manner."  He  also  makes  the  following 
disclaimer:  "I  am  aware  that  cyanides  have  already  been  used  in 
the  extraction  of  gold;  also  that  gold-bearing  ores  have  been  dis- 
integrated in  the  presence  of  heat  by  various  chemicals.  This  I  do 
not  claim."  The  mixture  claimed  consists  of  about  16  parts  of 
cyanide  of  potassium  to  1  part  of  glacial  phosphoric  acid,  with 
sufficient  water  to  form  a  thick  pulp  with  the  raw  gravel.  This 
would  undoubtedly  dissolve  in  some  cases  considerable  amounts  of 
gold,  but  that  circumstance  seems  to  have  entirely  escaped  the 
inventor's  observation. 

Simpson's  Patent:  Cyanide  with  other  Chemicals  as  Gold 
Solvent.  —  A  patent  which  has  much  more  direct  bearing  on  the 
subject  and  which  may  legitimately  be  regarded  as  in  some 
respects  an  anticipation  of  the  process  of  MacArthur  and  Forrest 
is  that  of 

Jerome  W.  Simpson:  U.  S.  patent,  No.  323,222: 

Filed  Oct.  20,  1884;  issued  July  28,  1885: 

"Process  of  Extracting  Gold,  Silver,  and  Copper  from  their  Ores." 

The  crushed  ore  is  to  be  treated  with  certain  salts  in  solution 
adapted  to  combine  chemically  with  the  metal  and  form  therewith 
a  soluble  salt.  After  thorough  agitation,  the  solid  matter  is  allowed 
to  settle  and  a  piece  or  plate  of  zinc  is  to  be  suspended  in  the  clear 
liquid,  "which  causes  the  metal  dissolved  in  the  salt  solution  to 
be  precipitated  thereon,  from  which  it  can  be  removed  by  scraping 
or  by  dissolving  the  zinc  in  sulphuric  or  hydrochloric  acid.  The 
precipitated  metal  may  then  be  melted  into  a  button." 

The  salt  solution  referred  to  consists  of  "  one  pound  of  cyanide  of 
potassium,  one  ounce  carbonate  of  ammonia,  one-half  ounce 
chloride  of  sodium,  and  16  quarts  of  water,  or  other  quantities 
in  about  the  same  proportions."  It  would  appear  that  the  car- 
bonate of  ammonia  was  added  as  a  solvent  for  copper,  and  the 
chloride  of  sodium  as  a  solvent  for  silver;  for  in  the  case  of  ores 
containing  only  gold  and  copper  he  omits  the  chloride  of  sodium, 
and  for  ores  rich  in  silver  he  employs  a  proportionately  larger 


EARLY  HISTORY  OF  THE  CYANIDE  PROCESS  23 

quantity  of  this  salt.  He  also  disclaims  the  exclusive  use  of  cya- 
nide as  a  solvent,  as  follows: 

"  I  am  aware  that  cyanide  of  potassium,  when  used  in  connec- 
tion with  an  electric  current,  has  been  used  for  dissolving  metal, 
and  also  that  zinc  has  been  employed  as  a  precipitant,  and  the  use 
of  these  I  do  not  wish  to  be  understood  as  claiming  broadly." 
He  also  disclaims  the  exclusive  use  of  carbonate  of  ammonia  but 
claims: 

"  1.  The  process  of  separating  gold  and  silver  from  their  ores 
which  consists  in  subjecting  the  ore  to  the  action  of  a  solution  of 
cyanide  of  potassium  and  carbonate  of  ammonia,  and  subsequently 
precipitating  the  dissolved  metal,  substantially  as  set  forth. 

"2.  The  process  of  separating  metals  from  their  ores,  to  wit: 
subjecting  the  ore  to  the  action  of  a  solution  of  cyanide  of  potas- 
sium, carbonate  of  ammonia,  and  chloride  of  sodium,  and  subse- 
quently precipitating  the  dissolved  metals." 

The  addition  of  these  small  quantities  of  other  chemicals  almost 
suggests  that  they  were  introduced  because  Simpson  doubted 
the  validity  of  a  patent  based  on  the  use  of  cyanide  alone.  With 
regard  to  this  process  it  may  be  remarked  that  the  solution 
specified  is  inconveniently  strong  in  cyanide,  and  that  the  precipi- 
tation process,  if  carried  out  as  described,  would  be  very  inefficient. 
It  is  nevertheless  possible  that  if  the  process  had  been  introduced 
on  a  working  scale  it  might  eventually  have  been  so  modified  as  to 
become  a  practical  success. 

Alleged  Anticipations  of  the  Cyanide  Process.  —  Caveats  cover- 
ing the  use  of  cyanides  for  extracting  precious  metals  are  alleged 
to  have  been  taken  out  by  Endlich  and  Muhlenberger,  in  1885, 
and  by  Louis  Jan  in,  Jr.,  in  1886,  but  no  definite  particulars  are 
available  with  regard  to  these.  It  is  rather  curious  to  note  that 
both  Endlich  and  Janin  write  in  a  disparaging  way  about  the  pros- 
pects of  cyanide  as  a  commercially  successful  solvent  of  gold  and 
silver  (see  Eng.  and  Min.  Journ.,  L,  685  and  LI,  86).  That  the 
practical  difficulties  in  the  way  of  the  application  of  cyanide  as  a 
solvent  had  not  been  overcome  at  the  time  of  the  MacArthur-For- 
rest  patents,  may  be  judged  from  the  following  remarks  of  Janin 
(ibid.,  L,  685),  from  a  letter  dated  Nov.  24,  1890: 

"To  sum  up  the  disadvantages  of  the  cyanide  process  in  a 
nutshell,  I  will  say  that  to  extract  a  reasonable  percentage  of  the 
gold  and  silver,  so  great  an  excess  of  cyanide  is  required  that  the 


24  THE  CYANIDE  HANDBOOK 

extraction  is  no  longer  economical  or  profitable.  Moreover,  if 
this  excess  is  used,  it  is  impossible  to  completely  precipitate  by  the 
means  advocated  by  the  MacArthur-Forrest  people.  In  fact,  as  a 
means  of  extracting  gold  I  can  more  conscientiously  recommend 
aqua  regia  than  potassium  cyanide." 

(C)   INTRODUCTION    OF    THE    MACARTHUR-FORREST    PROCESS 

Researches  on  Gold  Solvents  by  the  MacArthur-Forrest  Syndicate. 
—  We  have  now  traced  the  history  of  cyanide  in  its  application  to 
the  treatment  of  gold  and  silver  as  far  as  the  year  1886.  In  this 
year  experiments  were  being  made  in  Glasgow  by  a  research 
syndicate  consisting  of  J.  S.  MacArthur,  R.  W.  Forrest,  W.  Forrest, 
and  G.  Morton,  for  the  purpose  of  investigating,  and  if  possible 
developing  into  a  commercial  success,  a  method  of  ore  treatment 
known  as  the  "Cassel  Gold-Extracting  Process."  An  interesting 
account  of  the  steps  which  led  to  the  successful  application  of 
cyanide  in  the  treatment  of  ores  as  a  result  of  these  experiments  is 
given  by  J.  S.  MacArthur,1  in  a  paper  read  before  the  Scottish 
Section  of  the  Society  of  Chemical  Industry,  March  7,  1905,  from 
which  a  few  extracts  may  here  be  given.  The  process  under  inves- 
tigation depended  on  the  solvent  action  of  chlorine  generated 
electrolytic  ally  in  an  alkaline  solution.  It  was  found,  however, 
that  such  solvents  attacked  the  base  metals  in  the  ore  in  preference 
to  the  gold.  Attempts  were  made  to  dissolve  the  gold  and  limit 
the  action  on  base  metals  by  adding  chlorine  or  bromine,  without 
the  electric  current,  and  introducing  a  salt  which  would  not  absorb 
Cl  or  Br,  nor  precipitate  gold,  but  which  would  precipitate  base 
metal  compounds.  Bleaching-powder,  borax,  and  bicarbonate  of 
soda  were  found  to  partially  answer  this  purpose,  but  even  with 
this  addition  the  action  of  the  halogen  was  directed  rather  against 
the  base  metal  than  the  gold.  The  efforts  of  the  syndicate  were 
therefore  directed  to  finding  a  gold  solvent  that  would  not  be  a 
base-metal  solvent.  This  condition  naturally  pointed  to  some  alka- 
line or  neutral  solution.  In  making  these  tests  it  was  decided  not  to 
rely  on  the  method  of  taking  the  difference  between  original  assay 
of  ore  and  final  assay  of  residue  as  indicating  gold  extracted,  but 
in  all  cases  the  gold  was  to  be  precipitated  from  its  solution  and 

i  "Journ.  Soc.  Chem.  Ind.,"  XXIV,  311:  "Gold  Extraction  by  Cyanide: 
a  Retrospect." 


EARLY  HISTORY  OF  THE  CYANIDE   PROCESS  25 

recovered  in  a  visible  form,  so  that  it  could  be  actually  handled  and 
weighed,  sulphureted  hydrogen  being  used  as  the  precipitant. 

Cyanide  Extraction  Trials.  —  "  Among  the  various  solvents  on 
our  program  for  trial,  we  had  included  potassium  cyanide,  and  in 
November,  1886,  we  tried  the  effect  of  it  on  the  tailings  of  one  of 
the  Indian  gold  mines,  and,  as  usual,  treated  the  solution  with 
H2S  for  recovery  of  the  gold;  and  getting  none,  we  passed  on  to  our 
next  solvent,  meanwhile  observing  our  rule  of  labeling  the  residue 
and  laying  it  aside.  We  had  neglected  to  notice  that  H2S  did  not 
precipitate  gold  from  its  solution  in  cyanide,  and  thus  our  experi- 
ment was  for  the  time  literally  relegated  to  the  shelf.  About  eleven 
months  after,  I  had  occasion  to  devise  a  rapid  method  of  gauging 
approximately  the  gold  contents  in  weak  solutions  of  gold  chloride, 
and  used  for  the  purpose  tin  chloride  to  produce  the  well-known 
'purple  of  Cassius.'  One  solution  that  I  had  to  test  contained 
mercury,  and  using  potassium  cyanide  to  separate  the  mercury 
and  the  gold,  I  was  apprised  of  the  fact  that  H2S  did  not  precipitate 
gold  from  its  cyanide  solution.  Instantly  my  mind  reverted  to 
the  experiment  carried  out  nearly  a  year  before,  and  I  saw  that  it 
might  have  been  successful  without  the  success  being  recognized. 
Immediately  a  sample  of  rich  concentrates  from  a  Californian  mine 
was  treated,  and  on  this  occasion  we  examined  the  residue  rather 
than  the  solution,  and  found  a  high  percentage  of  extraction.  A 
sample  of  poor  concentrates  from  India  was  now  treated,  and  again 
a  high  extraction  was  obtained.  The  results  were  startling.  We 
unearthed  the  residues  from  the  old  experiments  (all  our  work  was 
done  in  duplicate),  and  to  our  intense  satisfaction  we  found  that 
they  too  had  transferred  their  gold  to  the  cyanide  solution.  There 
was  now  no  doubt  about  the  importance  of  the  discovery,  and  at 
once  a  provisional  specification  was  drafted  and  lodged." 

Mac  Arthur-Forrest  First  Patent.  —  The  provisional  specifi- 
cation of  the  English  patent,  No.  14,174,  was  lodged  Oct.  19, 
1887,  by  J.  S.  MacArthur,  R.  W.  Forrest  and  W.  Forrest,  and 
the  complete  specification  taken  out  July  16,  1888,  entitled: 
"Improvements  in  Obtaining  Gold  and  Silver  from  Ores  and 
other  Compounds."  The  essential  points  in  which  this  patent 
differs  from  those  of  previous  inventors  above  alluded  to,  are: 

1.  The  solution  of  the  gold  and  silver  is  to  be  effected  by  means 
of  a  liquid  to  which  a  cyanide  alone  is  added,  without  the  aid  of  an 
electric  current  or  of  other  chemicals. 


26  THE  CYANIDE  HANDBOOK 

2.  The  patentees  emphasize  the  use  of  dilute  in  preference  to 
strong  solutions  for  accomplishing  their  purpose. 

3.  Certain  definite  relations  are  specified  between  the  quanti- 
ties of  ore,  values  in  gold  and  silver,  and  strength  and  quantity  of 
solution,  which,  however,  were  not  adhered  to  in  practice  and 
cannot  be  regarded  as  being  essential  to  the  process. 

4.  Cyanogen  gas  is  mentioned  (probably  in  error)  as  one  of 
the  solvents  claimed. 

The  following  extracts  from  the  specification  will  illustrate 
these  points: 

(1)  Nature  of  the  Solvent.     "In  carrying  out  the   invention, 
the  ore  or  other  compound  in  a  powdered  state  is  treated  with  a 
solution   containing   cyanogen   or   cyanide    (such   as   cyanide   of 
potassium,  or  of  sodium,  or  of  calcium),  or  other  substance  or 
compound  containing  or  yielding  cyanogen." 

(2)  Use  of  dilute  solutions.     "  In   practice,  we   find  the  best 
results  are  obtained  with  a  very  dilute  solution,  or  a  solution  con- 
taining or  yielding  an  extremely  small  quantity  of  cyanogen  or  a 
cyanide,  such  dilute  solution  having  a  selective  action  such  as  to 
dissolve  the  gold  or  silver  in  preference  to  the  baser  metals." 

(3)  Relation   between    quantities   of   ore,    solution,    etc.     "  In 
preparing  the  solution  we  proportion  the  cyanogen  to  the  quantity 
of  gold  or  silver,  or  gold  and  silver,  estimated  by  assay  or  other- 
wise to  be  in  the  ore  or  compound  under  treatment,  the  quantity 
of  a  cyanide  or  cyanogen-yielding  substance  or  compound  being 
reckoned  according  to  its  cyanogen.  ...  In  dealing  with  ores  or 
compounds  containing,  per  ton,  20  ounces  or  less  of  gold  or  silver, 
or  gold  and  silver,  we  generally  use  a  quantity  of  cyanide  the  cyan- 
ogen of  which  is  equal  in  weight  to  from  one  to  four  parts  in  every 
thousand  parts  of  the  ore  or  compound,  and  we  dissolve  the  cyanide 
in  a  quantity  of  water  of  about  half  the  weight  of  the  ore.    In  the 
case  of  richer  ores  or  compounds,  whilst  increasing  the  quantity  of 
cyanide  to  suit  the  greater  quantity  of  gold  or  silver,  we  also 
increase  the  quantity  of  water  so  as  to  keep  the  solution  dilute." 

(4)  Use  of  cyanogen  ,gas.      "In   using   free   cyanogen,    the 
cyanogen  obtained  as  a  gas  in  any  well-known  way  is  led  into  water 
to  form  the  solution  to  be  used  in  our  process;  or  any  suitable 
known    mode    of    setting    cyanogen    free  in    solution    may    be 
employed." 

Reference  is  made  in  the  specification  to  the  use  of  agitation, 


EARLY  HISTORY  OF  THE  CYANIDE   PROCESS  27 

pressure,  and  increased  temperature  as  aids  to  extraction,  but  no 
claims  are  made  in  respect  to  these. 

No  special  means  of  precipitation  is  described  in  this  patent, 
but  the  following  statement  is  made:  "  When  all  or  nearly  all  the 
gold  or  silver  is  dissolved,  the  solution  is  drawn  off  from  the  ore  or 
undissolved  residue,  and  is  treated  in  any  suitable  known  way,  as, 
for  example,  with  zinc,  for  recovering  gold  and  silver.  The  residu- 
ary cyanogen  compounds  may  also  be  treated  by  known  means  for 
regeneration  or  reconversion  into  a  condition  in  which  they  can  be 
used  for  treating  fresh  charges  of  ores  or  compounds." 

The  solvents  enumerated  are:  "  Any  cyanide  soluble  in  water, 
.  .  .  such  as  ammonium,  barium,  calcium,  potassium  or  sodium 
cyanide,  or  a  mixture  of  any  two  or  more  of  them.  Or  any  mix- 
ture of  materials  may  be  taken  which  will  by  mutual  action  form 
cyanogen  or  a  substance  or  substances  containing  or  yielding 
cyanogen." 

Original  Claim.  —  The  first  claim  made  was:  "The  process  of 
obtaining  gold  and  silver  from  ores  and  other  compounds,  con- 
sisting in  dissolving  them  out  by  treating  the  powdered  ore  or 
compound  with  a  solution  containing  cyanogen  or  a  cyanide  or 
cyanogen-yielding  substance,  substantially  as  hereinbefore  de- 
scribed." 

Amended  Claim.  —  In  consequence  of  litigation,  this  was 
modified  so  as  to  apply  only  to  dilute  solutions  and  the  amended 
claim  (Aug.  20,  1895)  read  as  follows:  "Having  now  particu- 
larly described  and  ascertained  the  nature  of  our  said  invention, 
and  in  what  manner  the  same  is  to  be  performed,  we  declare  that 
we  do  not  claim  generally  the  use  of  solutions  of  any  strength,  but 
what  we  claim  is: 

"  1.  The  process  of  obtaining  gold  and  silver  from  ores  and 
other  compounds,  consisting  in  dissolving  them  out  by  treating 
the  powdered  ore  or  compound  with  a  dilute  solution  containing 
cyanogen  or  a  cyanide  or  cyanogen-yielding  substance,  substan- 
tially as  hereinbefore  described,  and  subject  to  the  above  disclaiming 
note:1 

Mac  Arthur-Forrest  Second  Patent.  —  On  July  14,  1888,  another 
patent  was  applied  for  by  Mac  Arthur  and  Forrest:  Eng.  patent 
No.  10,223,  entitled,  "Improvements  in  Extracting  Gold  and 
Silver  from  Ores  and  other  Compounds." 

Use  of  Alkalis.  —  After  referring  to  their  previous  patent,  they 


28  THE  CYANIDE  HANDBOOK 

describe  the  use  of  alkalis,  such  as  potash  or  lime,  for  neutralizing 
the  ore  previous  to  cyanide  treatment;  also  various  methods  of 
treatment  by  agitation,  grinding  in  pan-mills,  and  percolation  in 
tanks  with  permeable  false  bottoms,  are  indicated.  The  method 
of  precipitation  is  then  described  as  follows: 

Zinc  Precipitation.  —  "  The  separated  solution  is  next  made  to 
pass  through  a  mass  of  metallic  zinc  in  a  state  of  fine  division.  We 
find  that  the  best  results  are  obtained  in  this  part  of  the  process 
when  the  zinc  has  been  freshly  divided  by  mechanical  or  other 
means,  so  that  its  surfaces  are  as  purely  metallic  as  possible;  and, 
further,  when  the  quantity  or  mass  of  zinc  employed  is  such  that 
the  solution  has,  in  passing  through  it,  ample  opportunity  for 
being  thoroughly  acted  on. 

"  The  zinc  to  be  used  is  reduced  to  the  desired  state  of  fine  divi- 
sion by  any  suitable  means.  The  degree  of  division  is,  preferably, 
such  as  is  obtainable  by  shaving  or  by  cutting  thin  strips  or  very 
small  pieces  or  grains,  by  means  of  a  turning  tool,  circular  saw  or 
other  suitable  tool,  from  cakes  or  blocks  of  zinc  of  convenient  size. 
By  another  method,  the  zinc  is  brought  into  the  desired  state  of 
fine  division  by  passing  it  in  a  molten  state  through  a  fine  sieve 
and  allowing  it  to  fall  into  water.  In  order  to  obtain  the  best 
results  the  finely  divided  zinc  should  be  used  as  soon  as  possible 
after  it  has  been  produced." 

The  use  of  zinc  in  this  form  is  also  suggested  as  applicable  to 
other  gold-  and  silver-extracting  processes,  in  which  the  metals 
are  dissolved,  not  as  cyanides  but  as  chlorides,  bromides,  thiosul- 
phates  or  sulphates. 

"  After  separation  of  the  solution  the  precious  metals  may  be 
separated  from  zinc  by  distillation.  Or  the  larger  portion  of  the 
precious  metals  may  be  separated  from  zinc  by  sieving  (by  prefer- 
ence under  water),  when,  with  a  suitable  sieve,  the  greater  part 
of  the  precious  metals  will  pass  through,  the  greater  part  of  the 
zinc  being  left  on  the  sieve." 

The  claims  made  are:  (1)  "In  processes  for  extracting  gold  and 
silver  from  ores  or  other  compounds  by  means  of  a  cyanide  or 
cyanogen  compound,  the  preparatory  treatment  of  the  ores  or 
compounds  with  an  alkali  or  alkaline  earth,  substantially  as  and 
for  the  purposes  hereinbefore  described. 

(2)  "  In  precipitating  gold  and  silver  from  cyanide,  chloride, 
bromide,  thiosulphate,  or  other  similar  solutions  by  means  of  zinc, 


EARLY  HISTORY  OF  THE  CYANIDE   PROCESS  29 

the  employment  of  the  zinc  as  freshly  prepared  in  a  state  of  fine 
division,  substantially  as  hereinbefore  described. 

(3)  "  The  process  for  extracting  and  recovering  gold  and  silver 
from  ores  and  other  compounds,  consisting  in  first  treating  same 
with  an  alkali  or  alkaline  earth,  then  extracting  the  gold  by  means 
of  a  cyanide  or  cyanogen  compound,  and  finally  precipitating  the 
gold  and  silver  by  means  of  zinc  as  freshly  prepared  in  a  state  of 
fine  division,  all  substantially  as  hereinbefore  described." 

It  will  be  noted  that  no  broad  claim  to  the  use  of  zinc  as  a 
precipitant  is  made,  which  would  of  course  be  untenable,  but  only 
to  the  special  form  of  the  metal  found  suitable  in  this  process,  the 
discovery  of  which  is  described  by  MacArthur  in  the  paper  which 
we  have  already  referred  to.1 

Discovery  of  Precipitation  by  Zinc  Turnings.  —  "  We  knew  well 
that  zinc  precipitated  gold  from  its  cyanide  solution;  but  it  re- 
mained to  make  this  reaction  industrially  applicable.  We  used 
various  forms  of  finely-divided  zinc  with  more  or  less  advantage; 
but  a  picture  of  some  fine  zinc  shavings,  bought  with  other  things 
in  a  shilling  box  of  chemicals  in  my  boyish  days,  haunted  my  mind, 
and  repeatedly  I  described  it  to  one  of  the  works  foremen  without 
effect,  until  one  day,  when  making  a  zinc  case  for  packing  cyanide, 
he  made  a  shaving  by  a  sharp  tool  and  came  asking  me  if  this  was 
what  I  wanted.  My  reply  was  '  Yes/  and  in  half  an  hour  he  had 
prepared  the  first  bundle  of  zinc  shavings  for  gold  precipitation  — 
the  pioneer  bundle  of  hundreds  of  tons  of  this  flimsy  but  useful 
material." 

American  Patents:  (Mac Arthur-Forrest).  —  During  the  year 
1888,  patents  were  taken  out  in  most  of  the  important  mining 
countries  of  the  world,  covering  the  points  included  in  the 
two  just  discussed.  The  American  patents  are:  (1)  U.  S.  Patent, 
No.  403,202,  May  14,  1889;  referring  to  the  dissolving  process; 
and  (2)  U.  S.  Patent,  No.  418,137,  Dec.  24,  1889;  referring  to 
the  precipitation  process. 

The  former  of  these  differs  in  several  respects  from  the  British 
patent:  it  specifies  more  particularly  the  classes  of  ore  which  had 
not  previously  been  satisfactorily  or  profitably  treated,  and  to 
which  the  cyanide  process  may  be  applied  with  advantage;  and 
it  also  emphasizes  the  points  in  which  the  process  differs  from  those 
of  Rae,  Simpson,  and  other  inventors,  as  follows: 

>  J.  S.  MacArthur,  "  Journ.  Soc.  Chem.  Ind.,"  XXIV,  313. 


30  THE  CYANIDE   HANDBOOK 

"  By  treating  the  ores  with  the  dilute  and  simple  solution  of  a 
cyanide,  the  gold  or  silver  is,  or  the  gold  and  silver  are,  obtained 
in  solution,  while  any  base  metals  in  the  ores  are  left  undissolved, 
except  to  a  practically  inappreciable  extent;  whereas,  when  a 
cyanide  is  used  in  conjunction  with  an  electric  current,  or  in  con- 
junction with  another  chemically-active  agent,  such  as  carbonate 
of  ammonium  or  chloride  of  sodium  or  phosphoric  acid,  or  when 
the  solution  contains  too  much  cyanide,  not  only  is  there  a  greater 
expenditure  of  chemicals  in  the  first  instance,  but  the  base  metals 
are  dissolved  to  a  large  extent  along  with  the  gold  or  silver,  and 
for  their  subsequent  separation  involve  extra  expense,  which  is 
saved  by  our  process."  Further  particulars  are  given  as  to  the 
nature  of  the  containing  vessel,  and  as  to  mechanical  aids  to  extrac- 
tion. 

The  proportions  of  ore,  solution,  etc.,  are  the  same  as  in  the 
British  patent,  but  a  maximum  strength  is  given  and  the  claim  is 
limited  to  solutions  not  exceeding  this,  being  as  follows:  "The 
process  of  separating  precious  metal  from  ore  containing  base 
metal,  which  process  consists  in  subjecting  the  powdered  ore  to 
the  action  of  a  cyanide  solution  containing  cyanogen  in  the  pro- 
portion not  exceeding  eight  parts  of  cyanogen  to  one  thousand 
parts  of  water."  (This  would  be  equivalent  to  2  per  cent.  KCN.) 

Among  the  methods  of  recovering  gold  and  silver  from  the 
solution,  the  process  of  treating  it  with  sodium  amalgam  is  referred 
to. 

Introduction  of  the  Process.  —  Arrangements  were  now  made 
in  the  chief  mining  countries  to  introduce  the  process  on  a  practical 
basis:  the  first  works  on  a  commercial  scale  seem  to  have  been 
those  at  Karangahake,  New  Zealand,  established  in  1889.1 

In  the  early  part  of  1890,  the  Cassel  Company  established  an 
experimental  plant  near  the  old  Salisbury  Battery,  at  the  Natal 
Spruit,  near  Johannesburg,  Transvaal,  where  tailings  and  concen- 
trates were  treated  in  agitation  vats,  the  contents  of  which  were 
afterwards  discharged  on  to  suction  filters  and  the  liquid  drawn  off 
precipitated  by  zinc  shavings.  In  April,  1890,  these  works  were 
in  regular  operation,  and  the  results  were  so  successful  that  a 
plant  on  a  commercial  scale  was  established  in  the  latter  part  of 
the  year  at  the  Robinson  Mine,  Johannesburg. 

i  Large  scale  tests  were  made  on  ore  from  the  Crown  Mines  (New  Zealand) 
in  1888. 


EARLY  HISTORY  OF  THE  CYANIDE  PROCESS  31 

Importance  of  the  Cyanide  Process  in  Metallurgy.  —  Since 
then  the  process  has  spread  to  every  gold  and  silver  mining  dis- 
trict in  the  world,  with  few  exceptions,  and  although  not  equally 
successful  with  every  class  of  ore,  it  may  fairly  be  claimed  that  its 
introduction  has  revolutionized  the  metallurgy  of  the  precious 
metals.  During  the  ten  years  from  1886  to  1896,  the  world's 
production  of  gold  was  doubled,  and  it  is  stated  that  in  the  period 
1896-1906  it  again  doubled,  mainly  through  the  introduction  of 
new  metallurgical  methods  in  which  the  use  of  cyanide  has  played 
a  leading  part.  "  In  1889  the  world's  consumption  of  cyanide  did 
not  exceed  50  tons  per  annum.  In  1905  the  consumption  was 
nearly  10,000  tons  per  annum,  of  which  the  Transvaal  gold  field 
took  about  one-third."  1 

A  royalty  was  at  first  charged  by  the  African  Gold  Recovery 
Company,  representing  the  Cassel  Company  (the  owners  of  the 
MacArthur-Forrest  patents)  in  South  Africa.  The  validity  of  the 
patent  was,  however,  disputed,  and  the  patents  were  finally  set 
aside  in  February,  1896  after  an  appeal  to  the  High  Court  of 
the  Transvaal.  It  must  be  admitted,  however,  that  although  the 
patents  may  have  been  technically  invalid,  the  application  of  the 
process  in  such  a  form  as  to  be  commercially  successful  was  chiefly 
due  to  the  energy  and  enterprise  of  MacArthur,  Forrest,  and  their 
associates. 

Further  Developments.  — •  The  improvements  since  introduced 
have  chiefly  taken  the  form  of  applying  well-known  mechanical 
devices  previously  used  in  other  connections,  as  adjuncts  in  the 
working  of  the  process.  Such  alterations  in  the  chemical  treatment 
as  have  been  suggested  have  as  a  rule  found  only  a  partial  and 
temporary  application;  they  have  generally  taken  the  form  of 
additions  of  oxidizers  or  other  reagents  to  the  ore  or  solution: 
these  so-called  improvements  will  be  referred  to  later  in  a  special 
section  dealing  with  them.  We  may,  however,  enumerate  the 
following  as  being,  perhaps,  the  most  interesting  develop- 
ments : 

1893.       The  Electric  Precipitation  Process. 
1895.       The  Bromocyanide  Process. 

Slimes  Treatment  by  Decantation. 

Aeration  of  Ore  and  Slimes. 

i  Frankland,  "Journ.  Soc.  Chem.  Ind.,"  XXVI,  175. 


32  THE  CYANIDE   HANDBOOK 

1 897.  Zinc-lead  Precipitation  Process. 

1898.  Slimes  Treatment  by  Filter  Presses. 

"          Roasting  Previous  to  Cyanide  Treatment. 
1902.       Lead  Smelting  Applied  to  Zinc  Precipitate. 

Economical  Fine  Grinding  of  Ore  as  a  preliminary  to 
Cyanide  Treatment. 


SECTION  II 
OUTLINE  OF  OPERATIONS  IN  THE  CYANIDE  PROCESS 

(A)     THE  DISSOLVING  PROCESS 

Stages  of  Cyanide  Treatment.  — •  Having  now  traced  the  history 
of  cyanide  treatment  as  far  as  its  establishment  on  a  practical 
basis  by  MacArthur  and  Forrest,  we  shall  proceed  to  give  a  brief 
summary  of  the  actual  operations  involved  in  the  application  of 
the  process,  leaving  the  details  for  discussion  in  later  chapters. 
As  in  all  metallurgical  processes  for  the  treatment  of  ores,  the 
material  must  undergo  a  preliminary  crushing  or  disintegration  to 
render  the  metallic  particles  accessible  to  the  solvent.  After  the 
ore  has  been  thus  obtained  in  a  suitable  condition,  the  treatment 
takes  place  in  three  distinct  stages,  which  may  be  described  as: 

1.  The  dissolving  process; 

2.  The  precipitation  process; 

3.  The  smelting  process. 

Mechanical  Difficulties  in  Treatment  of  Crushed  Ore.  —  The 
method  of  treatment  to  be  adopted  in  the  dissolving  process,  and 
the  plant  and  appliances  used,  are  determined  largely  by  the 
physical  nature  of  the  material  to  be  dealt  with.  In  crushing 
any  kind  of  ore,  whatever  appliance  be  used,  certain  parts  will 
be  reduced  to  a  finer  state  of  division  than  others;  the  product 
is  never  homogeneous,  but  consists  of  particles  of  all  sizes,  from 
the  largest  that  will  pass  the  crushing  apparatus  to  the  minutest 
grains. 

Sands  and  Slimes.  —  At  an  early  stage  in  the  history  of  the 
process  it  was  found  that  the  treatment  of  the  crushed  material  as 
a  single  product  was  often  unsatisfactory.  The  methods  adopted, 
though  varying  greatly  in  detail,  may  be  roughly  classified  under 
two  heads — Agitation  and  Percolation.  In  the  agitation  process 
it  was  found  that  the  coarser  and  heavier  particles  showed  a 
tendency  to  settle  and  remain  stationary  in  corners  or  other  parts 

33 


34  THE  CYANIDE   HANDBOOK 

of  the  vessel  where  the  agitation  was  least  effective,  and  so  largely 
escaped  treatment.  In  the  percolation  system  the  finer  material 
showed  a  tendency  to  separate  in  certain  regions,  forming  bands  or 
masses  of  clay-like  material,  practically  impervious  to  the  solution, 
and  which  thus  also  escaped  effective  treatment.  Hence  the 
suggestion  naturally  arose  that  the  best  method  of  handling  the 
material  would  be  to  separate  the  coarser  and  heavier  portion  of 
the  crushed  ore  (technically  described  as  "  sands  ")  from  the  finer 
and  lighter  portion  (known  as  "slimes"),  and  to  treat  the  former 
by  percolation  and  the  latter  by  agitation.  This  idea  has  been 
almost  universally  carried  out  until  within  the  last  few  years, 
when  the  alternative  suggestion  of  crushing  the  whole  of  the 
material  so  fine  that  it  may  be  treated  satisfactorily  by  agitation 
has  been  rapidly  gaining  ground. 

Amalgamation.  — •  In  most  cases  the  ore,  after  crushing  and 
before  cyanide  treatment,  undergoes  some  form  of  amalgamation 
or  treatment  with  mercury,  the  usual  method  being  to  pass  the  ore 
as  it  leaves  the  stamp-batteries,  together  with  a  sufficient  quantity 
of  water,  in  a  thin  stream  over  sheets  of  copper  coated  with  mer- 
cury. The  latter  combines  with  and  arrests  the  coarser  particles 
of  precious  metal,  extracting  in  this  way  a  percentage  of  the  values 
which  varies  largely  with  different  kinds  of  ore,  and  may  perhaps 
average  about  60  per  cent. 

Hydraulic  Separation.  —  The  stream  leaving  the  amalgamated 
plates  then  passes  to  some  form  of  hydraulic  separator,  the  most 
usual  being  that  known  as  "  Spitzlutte,"  consisting  essentially  of  a 
pointed  box  with  a  central  partition,  and  an  outlet  at  the  bottom 
near  which  a  jet  of  water  is  introduced.  The  pulp  fed  in  at  the  top 
on  one  side  passes  downward  beneath  the  partition,  where  it  meets 
an  ascending  stream  of  water;  the  lighter  particles  are  carried 
away  and  overflow  on  the  opposite  side  at  the  top  of  the  box, 
while  the  coarser  and  heavier  particles  fall  through  the  outlet  at 
the  bottom.  The  pulp  may  be  passed  through  a  succession  of  such 
boxes  to  give  a  sufficiently  complete  separation  of  sands  and  slimes. 

Collection  of  Sands  for  Treatment.  —  When  the  sands  are  to  be 
treated  by  percolation  they  are  led,  usually,  into  a  collecting-vat, 
where  they  are  evenly  distributed  by  means  of  a  hose  or  by  some 
mechanical  device.  As  the  vat  fills,  the  surplus  water,  containing  a 
further  quantity  of  slime,  is  continuously  drawn  off.  When  the 
vat  has  been  thus  filled  with  sand,  the  contents  are  frequently 


OUTLINE    OF    OPERATIONS    IN   THE   CYANIDE    PROCESS     35 

prepared  for  cyanide  treatment  by  the  addition  of  alkali  (generally 
lime) ,  and  a  wash  of  water  or  very  weak  solution  is  given  in  order 
to  dissolve  the  alkali  and  distribute  it  to  every  part  of  the  charge. 
In  some  cases  the  cyanide  treatment  is  partially  carried  out  in  the 
collecting-vats,  but  usually  the  sand  is  transferred  through  dis- 
charge doors  at  the  bottom  of  the  collecting-vat  into  filter-tanks 
placed  underneath.  These  tanks  are  nearly  always  circular, 
and  constructed  of  wood  or  iron.  The  bottom  is  covered  by  a 
wooden  framework  on  which  rests  a  filter  composed  of  cocoanut 
matting  or  some  similar  material  covered  by  thick  canvas. 

Percolation  Process.  —  The  solution  is  led  by  iron  pipes  from 
the  storage-tank  to  the  top  of  the  filter-tank  and  allowed  to  flow 
on  until  the  charge  of  sand  is  completely  covered.  It  is  then  left 
standing  for  a  longer  or  shorter  period,  and  drawn  off  by  opening 
a  valve  in  a  pipe  beneath  the  filter  bottom;  the  liquid  thus  drained 
off  passes  either  direct  to  the  precipitation  boxes  or,  more  gener- 
ally, to  a  settling-tank,  where  any  suspended  matter  is  allowed  to 
subside,  and  from  whence  the  clear  liquid  is  drawn  off  for  precipita- 
tion. A  number  of  washes  in  succession  are  given  in  this  way,  the 
quantity  of  liquid  used,  strength  of  solution,  time  of  contact  and 
other  details  being  varied  according  to  the  nature  of  the  material. 
The  general  practice  may  be  described  somewhat  as  follows: 

1.  One  or  two  washes  of  very  weak  (alkaline)  solution,  for 
neutralizing  acid  substances  in  the  ore. 

2.  The  strong  solution  —  say  one-fifth  the  weight  of  charge  — 
usually  about   .25  per  cent.  KCy;  left  standing  6  to  12  hours  or 
more,  then  drained  as  completely  as  possible. 

3.  A  number  of  washes,  successively  weaker  in  cyanide  down  to 
.1  per  cent.  KCy. 

4.  A  final  wash  of  water,  or  the  weakest  solution  available. 
The  total  amount  of  solution  used  would  be  from  1  to  1^  times 

the  weight  of  the  dry  sand  in  the  charge;  total  time  of  treatment, 
4  to  8  days.  These  quantities  refer  to  tailings  from  ordinary 
siliceous  ores  after  amalgamation.  When  the  ore  is  treated 
"  direct"  (i.e.,  without  amalgamation),  or  when  rich  or  refractory 
material  is  treated,  the  quantities  and  strength  of  solution  and 
the  time  of  contact  may  vary  within  very  wide  limits. 

Collection  of  Slimes  for  Treatment.  —  The  slimes  carried  off  by 
the  overflow  from  the  spitzlutten  and  collecting-vats  are  carried, 
generally  by  means  of  wooden  launders,  to  a  suitable  vessel,  gener- 


36  THE  CYANIDE  HANDBOOK 

ally  a  large  pointed  box  (spitzkasten),  where  they  undergo  partial 
settlement,  in  order  to  remove  superfluous  water.  Lime  is  gener- 
ally introduced  either  in  the  battery  itself  or  into  the  stream  of 
pulp  leaving  the  battery,  which  has  the  effect  of  causing  the  fine 
particles  of  ore  quickly  to  coagulate  and  settle  when  the  rapid  flow 
of  the  liquid  is  arrested.  The  clear  water  from  the  spitzkasten  may 
be  pumped  back  to  the  battery  for  further  use,  while  the  thickened 
pulp  is  drawn  off  from  the  openings  at  the  bottom  of  the  spitzkas- 
ten and  passes  to  the  agitation  tanks,  where  it  is  generally  settled 
to  remove  a  further  quantity  of  water,  and  then  treated  with 
dilute  cyanide  solution,  with  alternate  agitation  and  settlement. 

Agitation  Process.  —  The  agitation  is  produced  either  by 
mechanical  stirrers  mounted  on  a  vertical  revolving  axis,  or  by 
injecting  air  under  pressure,  and  circulating  the  pulp  by  passing  it 
continuously  from  the  bottom  of  the  tank  through  a  centrifugal 
or  other  pump,  which  throws  it  back  into  the  same  tank.  The 
strength  of  cyanide  necessary  in  treating  slimes  is  in  general 
considerably  less  than  that  required  for  sands;  the  values,  being 
mostly  in  minute  particles,  dissolve  rapidly,  especially  when 
arrangements  are  made  for  effective  aeration. 

Separation  of  Dissolved  Values.  —  The  chief  difficulties  are 
encountered  in  the  mechanical  separation  of  the  solution  carrying 
the  dissolved  gold  and  silver,  from  the  residue.  Two  distinct 
methods  have  been  extensively  adopted  for  this  purpose;  these 
are: 

1.  The  decantation  process; 

2.  The  filter-press  process. 

Decantation  Process.  —  In  the  decantation  process,  which  is 
applicable  chiefly  to  very  low-grade  material,  such  as  the  Rand 
battery  slimes,  the  material  is  treated  in  very  large  tanks  by 
alternate  agitation  and  settlement;  the  clear  settled  solution 
is  drawn  off,  by  means  of  a  jointed  pipe,  from  the  surface  down  to 
the  level  of  the  slime-pulp.  Fresh  solution  is  then  added  and  the 
operation  repeated  two  or  three  times.  Sometimes  the  pulp  is 
finally  transferred  to  a  large  and  relatively  deep  tank,  where  the 
pressure  of  a  high  column  of  liquid  causes  the  slime  to  settle  with  a 
reduced  percentage  of  water;  after  several  successive  charges  have 
been  added,  the  clear  settled  solution  is  drawn  off  as  far  as  possible, 
and  the  residue,  carrying  say  30-40  per  cent,  of  moisture,  drawn 
off  at  the  conical  bottom  of  the  large  tank.  As  it  is  not  possible, 


OUTLINE    OF    OPERATIONS    IN    THE    CYANIDE   PROCESS     37 

from  economical  considerations,  to  give  more  than  one  or  two 
successive  agitations  and  decantations  on  the  same  charge,  the 
percentage  of  extraction  by  this  method  is  usually  somewhat  low, 
and  with  richer  material  the  alternative  process  of  filter-pressing 
has  been  found  more  advantageous. 

Filter-Press  Process.  —  In  the  filter-press  process,  after  the 
slime-pulp  has  had  a  preliminary  agitation  with  cyanide  solution, 
it  is  transferred  to  a  suitable  receiver,  whence  it  is  forced  by  means 
of  compressed  air  into  the  filter-presses,  consisting  of  a  number  of 
chambers  enclosed  by  metal  frames  and  plates,  so  arranged  that 
when  the  chambers  are  filled  with  the  slime-pulp,  liquid  (either 
cyanide  solution  or  water)  may  be  forced  through  them  under 
pressure,  thence  passing  through  filter-cloths  into  channels  con- 
nected with  the  outlet,  from  which  it  is  conveyed  to  a  settling- 
tank  and  thence  to  the  precipitation  boxes.  Various  types  of  press, 
operating  by  pressure  or  by  suction,  have  been  introduced,  and 
will  be  described  in  more  detail  in  a  special  section.  In  general,  it 
may  be  said  that  the  filter-press  process  involves  more  expense 
for  labor,  power,  etc.,  per  ton  of  material  treated,  than  the  decan- 
tation  process,  but  that  the  percentage  of  extraction  is  higher,  and 
the  time  of  treatment  less;  also  less  liquid  is  required,  an  important 
consideration  in  regions  where  water  is  scarce.  After  several 
washes  of  solution  and  water  have  been  thus  forced  through  the 
press,  the  latter  is  opened,  and  the  cakes  of  slimes,  containing  a 
much  lower  percentage  of  moisture  than  the  residues  of  the  decan- 
tation  process,  are  removed  and  discharged. 

Fine  Crushing  for  Cyanide  Treatment.  —  In  the  system  now 
coming  into  general  use  the  ore  is  crushed  rather  coarsely  in  the 
battery,  with  water  or  dilute  cyanide  solution  containing  sufficient 
lime  to  make  it  slightly  alkaline.  The  pulp  then  passes,  with  or 
without  previous  amalgamation,  through  a  "  tube  "  or  "  flint "  mill, 
consisting  of  a  revolving  steel  cylinder  with  a  suitable  lining  of 
some  hard  material,  and  about  half  filled  with  more  or  less  rounded 
flint  pebbles.  The  ore  is  effectively  and  economically  ground  in 
this  apparatus;  the  cylinder  is  set  in  a  slightly  inclined  position, 
and  the  pulp  passing  out  through  an  opening  at  the  lower  end  goes 
to  the  spitzkasten,  whence  the  coarser  portion  is  returned  to  the 
upper  end  of  the  tube-mill  to  be  reground.  The  fine  portion,  con- 
sisting almost  entirely  of  particles  small  enough  to  pass  a  sieve 
of  150  holes  to  the- linear  inch,  passes,  either  direct  or  after  ama.1- 


38  THE  CYANIDE  HANDBOOK 

gamation,  to  the  agitation  tanks,  the  whole  of  it  being  treated  as 
slimo  and  passed  through  filter-presses. 

It  will  be  seen  that  the  treatment  is  thus  much  simplified;  the 
high  initial  cost  of  leaching  and  decantation  plants  is  avoided,  with 
a  higher  percentage  of  extraction  and  an  increased  quantity  of  ore 
treated  per  month. 

Extraction  by  Cyanide  Process.  —  The  extraction  of  gold  and 
silver  varies,  according  to  the  nature  of  the  material,  from  under 
70  to  over  95  per  cent,  of  the  total  value :  many  ores  hitherto  con- 
sidered refractory  have  been  found  to  yield  a  high  percentage  after 
fine  grinding. 

Disposal  of  Residues.  —  The  residues  after  treatment  are  dis- 
charged either  by  shoveling  into  trucks,  or  by  various  mechanical 
devices,  or  by  sluicing. 

(B)     THE  PRECIPITATION  PROCESS 

Clarification  of  Solutions  before  Precipitation.  —  The  solutions 
drawn  off  from  the  leaching-tanks,  or  from  slime-treatment  tanks 
or  filter-presses,  usually  contain  a  certain  amount  of  siliceous  and 
other  matter  in  suspension,  which  it  is  desirable  to  remove  by  a 
preliminary  operation.  This  is  done  by  settlement  in  special 
tanks,  or  by  passing  the  liquor  through  small  filter-presses,  so  that 
only  perfectly  clear  liquid  enters  the  precipitation  boxes. 

Zinc-Boxes.  —  These  boxes  usually  consist  of  a  number  of 
compartments  so  arranged  that  the  solution  flows  upward  in  each 
compartment  through  a  mass  of  zinc  shavings,  then  over  a  parti- 
tion and  downward  through  a  narrow  space  to  the  bottom  of  the 
next  compartment,  where  it  again  ascends  through  a  mass  of 
zinc  shavings.  The  shavings  are  supported  on  perforated  remov- 
able trays,  so  that  any  precipitate  which  may  become  detached 
may  fall  to  the  bottom  of  the  box. 

Lead-Zinc  Couple.  — •  The  efficiency  of  precipitation  is  fre- 
quently increased  by  previously  immersing  the  shavings  in  lead 
acetate,  or  by  allowing  a  strong  solution  of  lead  acetate  to  drip 
slowly  into  the  liquid  at  the  head  of  the  boxes.  This  produces  a 
deposit  of  finely-divided  lead  on  the  zinc  and  probably  sets  up  an 
electrical  action  which  brings  about  the  rapid  replacement  of  gold 
or  silver  by  zinc  in  the  cyanide  solution. 

Conditions  for  Good  Precipitation.  —  The  essential  points  for 
effective  precipitation  are : 


OUTLINE   OF    OPERATIONS    IN    THE    CYANIDE    PROCESS      39 

1.  Sufficient  surface,  secured  by  cutting  the  zinc  into  long  nar- 
row strips. 

2.  Uniform  distribution  in  the  boxes,  so  as  to  allow  no  spaces 
or  channels  where  the  solution  could  pass  without  coming  into 
effective  contact  with  the  zinc. 

3.  Unimpeded  uniform  flow  of  liquid :  the  shavings  must  not  be 
so  fine,  or  so  tightly  packed,  that  the  liquid  cannot  freely  pass. 

4.  Sufficient  time  of  contact.    The  flow  of  liquid  through  the 
box  must  not  be  too  rapid. 

5.  A  sufficient  quantity  of  free  cyanide  in  the  solution  to  be 
precipitated. 

6.  A   slight  but  decided   alkalinity:    Insufficient  cyanide  or 
alkali  lead  to  the  formation  of  white  deposits,  probably  consisting 
of  cyanide,  ferrocyanide,  or  hydrate  of  zinc,  which  interfere  very 
seriously  with  the  precipitation  of  the  metals. 

7.  Absence  of  suspended  matter,  such  as  finely  divided  silica, 
ore  slimes,  etc.,  which  would  settle  on  the  zinc  and  also  impede 
precipitation. 

8.  Absence  of  large  accumulations  of  soluble  salts  of  the  base 
metals,  particularly  of  copper,  which  sometimes  forms  a  firmly 
adherent  layer  on  the  surface  and  completely  prevents  the  replace- 
ment of  gold  by  zinc. 

Disposal  of  Precipitated  Solution.  —  The  solution  leaving  the 
zinc-boxes  passes  usually  to  storage-tanks  or  sumps,  where  it  is 
made  up  to  the  required  strength  by  addition  of  fresh  cyanide,  and 
pumped  back  as  required  for  the  treatment  of  fresh  charges  of  ore. 

Accumulation  of  Zinc  in  Solution.  —  It  might  be  supposed  that, 
as  the  zinc  is  continually  dissolving  in  the  precipitation  boxes,  and 
the  same  liquid  is  repeatedly  used  in  the  treatment,  the  liquid 
would  become  gradually  saturated  with  salts  of  zinc.  It  is  gener- 
ally found,  however,  owing  to  reactions  which  will  be  discussed 
later,  that  the  accumulation  of  zinc  ceases  after  the  solutions  have 
been  in  use  for  some  time,  and  that  the  fresh  quantities  dissolved 
are  compensated  by  the  introduction  of  fresh  water  and  the  re- 
moval of  old  solution  in  the  moisture  of  the  discharged  residues. 

Alternative  Methods  of  Precipitation.  —  Other  methods  of  pre- 
cipitation have  frequently  been  suggested,  since  the  zinc  process, 
particularly  in  its  earlier  forms,  presented  certain  obvious  draw- 
backs. Only  two  of  these,  however,  have  found  any  extensive 
application,  viz.: 


40  THE  CYANIDE   HANDBOOK 

1.  Electric  precipitation; 

2.  Zinc-dust  precipitation. 

The  former  has  now  been  abandoned  in  favor  of  improved 
forms  of  the  zinc  process  in  all  but  a  few  localities,  and  the  latter 
may  be  said  to  be  still  on  its  trial. 

Electric  Precipitation.  —  The  electric  process  was  devised  by 
the  late  Dr.  Wernher  Siemens,  and  was  introduced  in  Russia  by 
A.  von  Gernet  about  the  same  time  that  the  Mac  Arthur-Forrest 
process  was  introduced  in  South  Africa.  Subsequently  (in  1893), 
von  Gernet,  representing  the  firm  of  Siemens  &  Halske,  of  Berlin, 
introduced  the  process  in  the  Transvaal,  and  for  several  years  it 
was  extensively  used.  The  method  then  employed  consisted  in 
electrolyzing  the  solutions  with  anodes  of  iron  and  cathodes  of 
sheet  lead,  the  gold  and  silver  being  deposited  on  the  latter,  while 
the  anodes  were  gradually  consumed  with  formation  of  soluble 
ferrocyanides,  Prussian  blue,  and  other  products.  The  cathodes 
were  removed  from  time  to  time  and  cupeled  for  recovery  of  the 
gold  and  silver. 

Advantages  and  Disadvantages  of  the  Process.  —  The  process 
presented  the  advantage  that  weaker  cyanide  solutions  could  be 
precipitated  than  was  at  that  time  possible  with  the  zinc  process; 
the  dirty  and  troublesome  operation  of  cleaning  up  the  zinc-boxes 
was  avoided,  and  the  bullion  was  obtained  in  a  purer  and  more 
marketable  form.  As,  however,  a  very  large  area  was  needed  for 
efficient  precipitation,  the  boxes  required  were  much  larger,  and 
in  general,  the  initial  outlay,  and  expenses  for  maintenance  and 
skilled  labor,  particularly  in  the  cupellation  of  the  bullion,  out- 
weighed these  advantages.  When  improved  forms  of  the  zinc 
process,  particularly  the  use  of  the  zinc-lead  couple,  were  intro- 
duced, the  electric  process  was  no  longer  able  to  hold  its  own, 
though  a  modification  of  it,  which  will  be  described  later,  is  still 
in  use  in  Mexico. 

Zinc-Dust  Precipitation.  —  The  use  of  zinc-dust  for  precipita- 
tion was  first  suggested  by  Sulman  and  Teed  (1895),  in  conjunc- 
tion with  their  bromocyanide  process.  It  has  been  used  to  a 
considerable  extent  in  America  in  conjunction  with  other  forms  of 
the  dissolving  process.  The  material  used  is  a  by-product  obtained 
in  the  distillation  of  commercial  zinc,  and  contains  a  certain 
amount  of  oxide,  which  is  sometimes  removed  by  preliminary 
treatment  with  ammonia  or  an  ammonium  salt.  Being  already  in 


OUTLINE    OF    OPERATIONS   IN  THE   CYANIDE    PROCESS     41 

a  very  fine  state  of  division,  it  presents  a  large  surface  and  hence 
forms  an  efficient  precipitant.  It  is  generally  agitated  with  the 
solution  in  a  special  tank,  the  agitation  being  obtained  by  forcing 
in  compressed  air.  It  has  been  stated,  however,  that  the  parti- 
cles of  zinc  become  coated  with  gold  in  such  a  manner  that  the 
zinc  is  largely  protected  during  the  subsequent  acid  treatment, 
and  hence  a  low  grade  of  bullion  is  produced. 

Consumption  of  Zinc.  —  The  consumption  of  zinc,  when  used 
in  the  form  of  shavings,  amounts  generally  to  0.3  Ib.  per  ton  of 
ore  treated;  when  in  the  form  of  dust,  the  consumption  is  some- 
times about  the  same,  but  often  much  higher.  The  precipitate 
obtained  by  zinc-dust  is  more  uniform  in  composition  and  may 
conveniently  be  pressed  into  cakes  prior  to  smelting. 

(C)     THE  SMELTING  PROCESS 

Nature  of  Zinc-Gold  Precipitate.  —  The  material  collected  when 
the  zinc-boxes  are  periodically  cleaned  up  consists  of  finely  divided 
gold  and  silver,  mixed  with,  and  perhaps  to  some  extent  actually 
alloyed  with,  metallic  zinc,  together  with  greater  or  smaller  quan- 
tities of  such  impurities  as  lead,  copper,  iron,  and  various  insoluble 
metallic  salts,  such  as  carbonates,  sulphates,  complex  cyanogen 
compounds,  silica,  alumina,  etc.  This  is  removed  from  the  unde- 
composed  zinc  shavings  as  much  as  possible  by  rubbing  on  a  sieve; 
the  coarse  zinc  remaining  on  the  sieve  is  returned  to  the  boxes, 
and  the  remainder,  usually,  is  passed  over  a  finer  sieve,  the  pro- 
ducts remaining  on  and  passing  this  sieve  being  described  as 
"  shorts  "  and  "  fines  "  respectively.  These  are  often  submitted  to 
separate  treatment. 

Acid  Treatment.  —  Formerly,  the  zinc-gold  precipitate  was 
usually  simply  dried,  and  smelted  direct  with  suitable  fluxes.  It 
is  now  customary,  however,  to  treat  it  with  dilute  sulphuric  acid, 
to  remove  as  much  as  possible  of  the  metallic  zinc  and  other  im- 
purities soluble  in  this  acid.  This  treatment  is  generally  carried 
out  in  a  wooden  vat,  and  is  aided  by  stirring  by  hand  or  mechani- 
cally, and  sometimes  by  heating  with  steam  or  otherwise.  The  vat 
should  be  provided  with  a  cover  and  the  operation  conducted  in  a 
good  draft,  so  that  the  very  poisonous  fumes  evolved  may  be 
rapidly  carried  off.  When  the  action  of  the  acid  is  complete  the 
precipitate  is  allowed  to  settle  and  the  clear  liquid  decanted.  One 
or  two  washes  are  given  with  hot  water  to  remove  zinc  sulphate 


42  THE  CYANIDE   HANDBOOK 

and  other  soluble  salts,  and  frequently  the  residue  is  put  through  a 
small  filter-press,  after  which  the  cakes  are  partially  dried  and 
smelted  with  fluxes. 

Roasting  of  Zinc-Precipitate.  —  Another  method  often  adopted 
instead  of,  or  in  conjunction  with,  acid  treatment  is  to  roast  the 
precipitate  in  a  small  reverberatory  furnace.  In  some  cases 
the  precipitate  is  intimately  mixed  with  niter  or  other  oxidizing 
agent  previous  to  roasting.  This  operation  may  be  carried  out 
either  before  or  after  acid  treatment.  It  is,  however,  supposed 
to  generally  involve  considerable  losses  of  gold  and  silver. 

Smelting.  —  The  precipitate,  after  undergoing  one  or  other  of 
these  preliminary  operations,  is  then  mixed  with  a  flux  consisting 
of  borax,  soda,  some  siliceous  material,  and  sometimes  fluor-spar 
and  an  oxidizing  agent.  The  fusion  is  generally  made  in  graphite 
crucibles,  but  preferably  with  a  clay  lining.  Various  types  of 
reverberatory  and  other  furnaces  have  been  used  in  place  of 
crucibles;  tilting  furnaces,  operating  in  the  manner  of  a  Bessemer 
converter,  have  also  been  used.  The  proportion  of  fluxes  is 
varied  according  to  the  nature  of  the  material  to  be  smelted,  and 
is  of  course  determined  largely  by  the  preliminary  treatment 
which  it  has  undergone.  Where  an  oxidizer  has  to  be  added 
manganese  dioxide  has  been  found  to  possess  some  advantages 
over  niter. 

Casting  the  Bullion.  —  Immediately  before  pouring,  the  bullion 
is  stirred  and  a  sample  taken.  The  slag  formed  consists  chiefly 
of  silicates  of  zinc  and  other  metals  still  present  after  the  acid  or 
other  treatment.  Where  the  fusion  has  been  properly  conducted, 
the  bullion  contains  900  to  950  parts  gold  and  silver  per  1000. 

The  slag  and  any  other  by-products  of  the  smelting  process 
should  be  tested  for  gold  and  silver;  they  frequently  contain 
sufficient  values  to  justify  working  over  again  by  special  processes. 

Lead  Smelting  of  Zinc  Precipitate.  —  Another  method  of  treat- 
ing the  zinc  precipitate,  which  has  been  adopted  with  much  success 
in  South  Africa  and  other  countries,  is  the  process  of  smelting  with 
lead,  introduced  by  P.  S.  Tavener.  The  precipitate  (with  or  with- 
out previous  acid  treatment  and  filter-pressing)  is  mixed  with 
litharge,  powdered  coal,  siliceous  slag  or  sand,  and  a  little  scrap- 
iron.  On  melting  in  a  suitable  furnace,  the  gold  and  silver  are 
obtained  as  an  alloy  with  lead;  the  slag,  carrying  the  zinc,  etc., 
is  tapped  off,  and  the  lead  bullion  cast  into  bars.  These  are  then 


OUTLINE    OF    OPERATIONS    IN    THE   CYANIDE  PROCESS     43 

cupeled  on  a  bone-ash  "test,"  and  the  litharge  formed  collected 
for  use  in  a  subsequent  operation.  The  cupeled  metal  is  then 
broken  up  and  remelted  with  borax  or  other  flux  in  clay  or  graph- 
ite crucibles. 

The  cost  of  this  process  is  said  to  be  very  much  less  than  that 
of  other  methods  of  smelting;  practically  all  by-products  are  used 
up,  and  the  comparatively  rich  slags  from  the  ordinary  fusion 
methods  can  be  utilized  as  fluxes  in  the  lead-smelting  process. 
The  slag  produced  in  the  fusion  for  lead  bullion  often  contains  less 
than  1  oz.  gold  per  ton. 

Refining  with  Oxygen.  —  The  suggestion  has  also  been  made  to 
refine  zinc  precipitate  by  passing  oxygen  gas  or  air  through  the 
molten  material,  as  in  the  refining  of  gold  by  chlorine.  A  number 
of  experiments  were  made  with  this  object  by  T.  K.  Rose,1  and 
some  attempts  have  been  made  to  apply  the  principle  in  practice, 
though  we  are  not  aware  that  it  has  been  regularly  adopted  as  yet. 

i  Rose,  Trans,  I.  M.  M.,  XIV,  378. 


PART  II 
CHEMISTRY 


SECTION  I 

CYANOGEN    AND    ITS    COMPOUNDS    WITH 
NON-METALS 

WE  shall  here  give  a  summary  of  the  modes  of  formation, 
physical  properties,  and  principal  reactions  of  the  more  important 
cyanogen  compounds,  but  we  shall  confine  the  discussion  prin- 
cipally to  the  inorganic  compounds  of  the  cyanogen  radical. 
Only  such  organic  derivatives  as  may  be  of  some  interest  and 
importance  in  connection  with  the  cyanide  process  or  with  the 
manufacture  of  cyanide  will  be  referred  to. 

For  convenience,  we  may  subdivide  this  discussion  of  cyan- 
ogen and  its  compounds  as  follows: 
Section  I  (pages  47-61). 
(a)    Cyanogen. 
(6)    Hydrocyanic  Acid. 

(c)    Compounds  of  Cyanogen  with  Non-metals. 
Section  II  (pages  62-83). 

(a)    Simple  Metallic  Cyanides,  including  easily  decomposed 

Double  Cyanides. 
Section  III  (pages  84-101). 

(a)    Metallic  Compounds  of  Complex  Cyanogen  Radicals. 
(6)    Cyanates,  Thiocyanates,  and  Related  Compounds. 
For  more  detailed  information  respecting  these  compounds  the 
reader  is  referred  to  such  works  as  Watt's  "  Dictionary  of  Chem- 
istry," revised  by  Morley  and  Muir,  or  to  the  articles  by  Joannis 
in  Fremy's  "Encyclopaedia." 

(A)    CYANOGEN    (CN) 
(Molecular  formula,  C2N2) 

Formation.  —  1.    By  dry  distillation  of  mercuric  cyanide: 
Hg(CN)2  =  Hg  +  (CN),. 

A  portion  of  the  cyanogen  polymerizes,  forming  the  brown  solid 
substance  paracyanogen  (CN)X. 

47 


48  THE  CYANIDE   HANDBOOK 

2.  By  dry  distillation  of  silver  cyanide: 

2AgCN  =  2Ag  +  (CN)2. 

3.  By  dry  distillation  of  mercuric  chloride  with  a  cyanide  or 
ferrocyanide : 

HgCl2  +  MCN  =  HgCl  +  MCI  +  CN. 

The  gas  obtained  is  in  some  cases  mixed  with  nitrogen 

4.  By  action  of  copper  salts  on  cyanides  in  solution 

2CuSO4  +  4KCN  =  Cu2(CN)2  +  2K2SO4  +  (CN)2. 

5.  Cyanogen  cannot  be  formed  by  direct  union  of  its  elements, 
but  it  is  a  product  of  certain  decompositions  of   compounds  of 
carbon  and  nitrogen  at  a  high  temperature.     Hence  it  is  one  of 
the  products  obtained  by  the  destructive  distillation  of  coal  in 
the  manufacture  of  illuminating  gas. 

Physical  Properties.  —  A  colorless  gas,  with  a  characteristic 
sharp  odor  resembling  bitter  almonds  and  prussic  acid;  it  is  very 
irritating  to  the  eyes,  and  poisonous. 

Density,  26  (H  ==  1),  or  1.8064  (air  =  1). 

Easily  condensed  to  a  transparent,  colorless,  very  mobile 
liquid,  boiling  under  ordinary  pressure  at  —  20.7°  C.,  having 
sp.  gr.  0.866  at  17.2°  C.,  and  refractive  index  1.316. 

Liquid  cyanogen  is  a  non-conductor  of  electricity;  it  has  no 
action  on  most  metallic  or  non-metallic  elements,  but  dissolves 
iodine  and  phosphorus. 

Cyanogen  gas  dissolves  to  some  extent  in  water  and  alcohol. 

Chemical  Characteristics.  —  Cyanogen  in  its  chemical  relation- 
ships may  be  regarded  from  two  different  points  of  view. 

(a)  In  many  reactions  it  plays  the  part  of  a  compound  radical; 
that  is  to  say,  it  behaves  as  though  the  nitrogen  and  carbon  con- 
stituted a  single  element  (often  represented  by  the  symbol  Cy). 
In  this  respect  it  is  in  many  ways  analogous  to  the  elements  of 
the  halogen  group. 

Compare   (CN)2  C12  Br2  I2 

KCN  KC1  KBr  KI 

AgCN  AgCl  AgBr  Agl 

Hg(CN)2  HgCl2  HgBr2  HgI2 

(6)  From  another  point  of  view  it  belongs  to  the  group  of 
organic  substances  known  as  nitrites,  which  may  be  regarded  a's 


CYANOGEN  AND   ITS  COMPOUNDS   WITH   NON-METALS      49 

derived  from  organic  acids  by  the  substitution  of  the  radical  CN 
for  C02H. 

Compare  Oxalic  acid  (CO2H)2  Cyanogen  (CN)2 

(oxalo-nitrile) 
Formic  acid  (H  -  CO2H)      Hydrocyanic  acid  (H  •  CN) 

(formo-nitrile) 
"  '       Acetic  acid  (CH3  •  CO2H)    Aceto  nitrile  (CH3  •  CN) 

Its  constitution  may  be  represented  by  the  symbol: 


Reactions.  —  1.    Decomposed  by  electric  arc  into  carbon  and 
nitrogen.     Not  decomposed  by  heat  alone. 

2.  Burns   (in   air  or  oxygen)   with  a  characteristic  purplish 
(peach-colored)    flame,    forming    carbon-dioxide    and    liberating 
nitrogen  : 

(CN)2  +  2O2  =  N2  +  2CO2. 

3.  Combines  with  hydrogen  when  heated  with  it  in  a  closed 
tube  or  under  the  influence  of  the  electric  current: 

(CN)2  +  H2  =  2HCN. 

Some  paracyanogen  is  also  formed. 

4.  The  alkali  metals  combine  slowly  with  cyanogen  at  ordi- 
nary temperatures,  and  with  incandescence  on  warming: 

(CN)2  +  K2  =  2KCN. 

Zinc  combines  slowly  on  heating.     Iron  decomposes  it  into  C 
and  N  at  a  red  heat.     Hg,  Cu,  Au,  and  Pt  have  no  direct  action. 

5.  Certain  non-metals  (S,  P,  I)  may  be  vaporized  unchanged 
in  an  atmosphere  of  CN.     Perfectly  dry  Cl  has  no  action  on  it, 
but  in   presence  of    moisture  a  yellowish  oil   is  deposited,   ap- 
parently a  mixture  of  chlorides  of  C  and  N,  and  also  a  white, 
solid,  aromatic  substance. 

6.  A    solution    of    cyanogen   in  water    gradually   undergoes 
decomposition,  turning  first  yellow,  then  brown,  and  depositing 
flakes  of  a  brown  substance.     The  first  action  is  probably  the 
formation  of  cyanic  arid  hydrocyanic  acids: 

2CN  +  H2O  =  HCNO  +  HCN. 

Further  decomposition  then  takes  place,   giving  ammonium 
oxalate,  ammonium  carbonate,  urea,  and  azulmic  acid  (the  insol- 


50  THE   CYANIDE   HANDBOOK 

uble  brown  substance),1  to  which  the  formula  C4H5N5O  has  been 
assigned. 

7.  Dry  H2S  gas  does  not  combine  with  cyanogen.      In  presence 
of  water  two  yellow  crystalline  substances  are  formed  having  the 
composition : 

(CN)2H2S  and  (CN)2  •  (H2S)2. 

The  first  is  formed  when  CN  is  in  excess;  the  second  when 
H2S  is  in  excess. 

Solutions  of  these  compounds  give  precipitates  with  various 
metallic  salts. 

8.  Concentrated  aqueous  HC1  converts  cyanogen  into  oxamide 
and  ammonium  oxalate,  thus  acting  as  a  "hydrating  agent": 

2CN  +  2H2O  =  CONH2  (oxamide). 

CONH2 
2CN  +  4H2O  =  CO2NH4  (ammonium  oxalate). 

CO2NH4 

Hydriodic  acid  gives  the  same  products  in  the  cold,  but  at  a 
high  temperature  gives  ammonia  and  ethane,  thus: 
2CN  +  12HI  =  2NH3  +  C2H6  +  6I2. 

9.  Alkalis  absorb  cyanogen  and  give  reactions  similar  to  those 
of  water: 

Cy2  +  2KOH  =  KCy  +  KCyO  +  H2O. 
[This  reaction  is  analogous  to  that  of  chlorine: 

C12  +  2KOH  =  KC1  +  KC10  +  H2O.] 

On  treatment  of  the  solution  with  strong  acids,  ammonium 
salts  are  formed  and  carbonic  acid  evolved  (by  decomposition 
of  the  cyanate) : 

KCNO  +  2HC1  +  H2O  =  KC1  +  NH4C1  +  CO2. 

A  slight  decomposition  occurs  without  addition  of  acids, 
according  to  the  reaction 

KCNO  +  KOH  +  H2O  =  K2CO3  +  NH3. 

When  excess  of  cyanogen  is  used,  the  solution  becomes  brown 
and  deposits  an  alkaline  azulmate. 

HgO  acts  like  caustic  alkalis:  if  a  current  of  cyanogen  be 
passed  into  water  containing  mercuric  oxide  in  suspension,  it 

i  Wohler,  "Pogg.  Ann.,"  Ill,  177.  Richardson,  "Philosophical  Magazine," 
XII,  339. 


CYANOGEN   AND   ITS   COMPOUNDS   WITH    NON-METALS        51 

yields  azulmic  acid,  ammonium  carbonate,  and  mercuric  cyanide 
and  oxycyanide. 

10.  Cyanogen  passed  over   potassium    carbonate   heated   to 
redness  gives  a  cyanate  and  cyanide: 

Cy2  +  K2C03  -  KCy  +  KCyO  +  CO2. 

11.  Dry  ammonia  gas  gradually  combines,  depositing  a  brown 
substance  (hydrazulmin)  : 

2(CN)2  +  2NH3  =  C4H6N6. 

Aqueous  ammonia  gives  azulmic  acid,  oxamide,  oxamic  acid, 
and  ammonium  oxalate. 

PARACYANOGEN     (CN)41 

Preparation.  —  This  polymer  of  cyanogen  is  obtained  by  heat- 
ing mercuric  cyanide  in  sealed  tubes  to  about  440°  C.;  also  by 
decomposition  of  hydrazulmin  (see  above)  : 
C4H6N6  =  (CN)4  +  2NH3. 

Properties.  —  A  blackish-brown,  light,  spongy  substance,  in- 
soluble in  water,  soluble  in  H2SO4,  and  precipitated  by  water  from 
the  solution  in  this  acid.  It  absorbs  and  condenses  gases. 

(B)    HYDROCYANIC  ACID  (HCy) 
(Prussic  Acid;  Hydric  Cyanide) 

Preparation.  —  1.  By  heating  mercuric  cyanide  with  hydro- 
chloric acid:  HgCyj  +  2HC1  =  HgCl2  +  2HCy 

The  vapor  may  be  rendered  anhydrous  by  passing  through 
tubes  containing  CaCO3  and  CaCl2,  which  remove  HC1  and  H20 
respectively.  Only  about  §  of  the  theoretical  quantity  is  ob- 
tained, owing  to  HgCl2  forming  a  compound  with  HCN.  The 
yield  may  be  increased  by  adding  NH4C1  to  the  mixture. 

2.  By  passing  H2S  over  HgCy2  or  AgCy,  heated  in  a  tube  to 
30°  -  40°  C. 


HgS  +  2HCy 

Lead  carbonate  is  used  to  absorb  excess  of  H2S. 
3.    By  action  of  dilute  sulphuric  acid  on  potassium  ferrocyanide 
(the  usual  method  of  preparation)  : 

3H2SO4  =  3KHSO4  +  KFeCy3  +  3HCy. 


1  The  formula  CN  -  C  =  C  -  CN  has  been  assigned  for  paracyanogen. 

I         i 

N  =  N 


52  THE   CYANIDE   HANDBOOK 

The  most  suitable  proportions  are: 

Potassium  ferrocyanide    8  parts 

Sulphuric  acid  (cone.) 9      " 

Water 12     " 

The  water  and  acid  should  be  mixed  before  hand,  and  cooled 
before  adding  to  the  powdered  ferrocyanide.  The  distilling- 
flask  is  heated  on  a  sand  bath  and  the  distillate  collected  in  a 
cooled  condenser. 

4.  By  the  action  of  acids  on  almost  any  metallic  cyanide:  e.g., 

KCy  +  HC1  =  KC1  +  HCy. 

This  class  of  reaction  has  been  utilized  for  preparing  dilute 
solutions  of  hydrocyanic  acid  of  known  strength  for  medicinal 
purposes. 

(a)   AgCy  +  HC1  -  AgCl  +  HCy  (Evcritt). 
(b}    PbCy2  +  H2SO4  =  PbSO4  +  2HCy  (Thomson). 

(c)  Tartaric  acid  acting  on  KCy  yields  a  nearly  insoluble  acid  potassium 
tartratc,  together  with  HCy  (Clarke). 

5.  When  a  series  of  electric  sparks  are  passed  through  a  mix- 
ture of  acetylene  and  nitrogen,  there  is  a  gradual  combination. 

Thus:  C2H2  +  N2  =  2HCN. 

Part  of  the  acetylene  decomposes  with  separation  of  carbon, 
unless  hydrogen  be  also  added. 

This  reaction  is  of  great  interest,  as  it  shows  how  cyanide 
compounds  may  be  formed  synthetically  from  their  elements: 
acetylene  is  produced  by  direct  union  of  carbon  and  hydrogen, 
when  electric  sparks  are  passed  between  carbon-points  in  an 
atmosphere  of  hydrogen. 

6.  By  passing  a  current  of  dry  ammonia  gas  over  carbon  con- 
tained in  a  porcelain  tube  heated  to  redness: 

C  +  2NH3  =  NH4CN  +  H2. 

By  passing  the  vapors  through  warm  dilute  sulphuric  acid 
HCy  is  liberated: 

NH4CN  +  H2SO4  =  NH4  •  HSO4  +  IICN. 

A   similar  reaction   takes   place  when    ammonia   and   carbon 
monoxide  are  passed  through  a  redrhot  tube: 
CO  +  2NH3  =  NH4CN  +  H2O. 

7.  By  dehydration  of  ammonium  formate: 

HCO2NH4  =  2H20  +  HCN. 


CYANOGEN  AND   ITS  COMPOUNDS   WITH   NON-METALS      53 

This  is  a  general  reaction  for  forming  the  "nitriles"  of  the 
corresponding  organic  acids;  thus,  ammonium  oxalate  yields 
cyanogen,  and  ammonium  acetate  yields  acetonitrile  when  acted 
on  by  a  dehydrating  agent. 

8.  By  destructive  distillation  of  ammonium  oxalate  or  oxam- 

lde:  (a)  (C02NH4)2  =  3H20  +  O  +  2HCN. 

(6)  (CO2NH2)2  =  H2O  +  3O  +  2HCN. 

9.  Hydrocyanic  acid  occurs  ready  formed  in,  or  is  a  product 
of  the  decomposition  of,  many  vegetable  substances.     The  ker- 
nels of  many  fruits,  such  as  peaches,  cherries,  almonds,  etc.,  and 
certain  leaves,  as  those  of  the  cherry-laurel,  contain  a  substance 
known  as  amygdalin,  which  is  decomposed  by  water  under  the 
influences  of  a  vegetable  ferment  (emulsin),  the  latter  undergoing 
no  apparent  change  in  the  reaction.     This  reaction  results  in  the 
formation  of  benzaldehyde,  glucose,  and  hydrocyanic  acid: 

CaoHwNOu  +  2H2O  =      C6H5  •  COH      +  2C6H12O6  +  HCN. 
Amygdalin  Benzaldehyde          Glucose 

10.  Hydrocyanic  acid  occurs  as  one  of  the  products  in  many 
reactions  of  organic  bodies;  e.g.,  in  the  action  of  ammonia  on 
chloroform: 


HCN. 

in  the  combustion  of  methylamine: 

CH3NH2  +  O2  =  2H2O  +  HCN; 
and  in  the  action  of  alkalis  on  nitrobenzene. 

The  anhydrous  acid  may  be  prepared  by  gently  heating  the 
aqueous  acid,  passing  the  vapors  through  vessels  containing  cal- 
cium chloride,  and  condensing  the  distillate  by  a  freezing  mixture. 

Physical  Properties.  —  A  volatile  colorless  liquid;  extremely 
poisonous.  Boiling-point  +  26.1°  C. 

When  allowed  to  evaporate  in  the  air,  a  portion  solidifies  in 
translucent  orthorhombic  prisms,  having  a  melting-point  —  14°  C. 

Density  of  liquid,    0.7058  at  7°  C. 
0.6969  at  18°  C. 

Density  of  vapor,    .97  to  .90  [air  =  1] 
13.5  [H  =  1]. 

Very  soluble  in  water.  The  addition  of  a  small  quantity  of 
water  to  the  anhydrous  acid  raises  the  boiling-point  and  lowers 
the  melting-point.  The  solution  of  HCN  in  water  is  accompanied 
by  condensation  and  lowering  of  temperature  (an  unusual  effect). 


54  THE  CYANIDE   HANDBOOK 

A  mixture  of  60  per  cent.  HCN  and  40  per  cent.  H2O  has  the  min- 
imum melting-point  (—  22.5°  C.). 

Reactions.  —  1.  Heated  in  closed  vessels  at  100°  C.,  it  forms 
a  black  mass,  which  when  afterward  heated  in  an  open  tube  at 
50°  C.  gives  off  NH4CN  and  (CN)2  leaving  a  carbonaceous  residue. 
A  current  of  HCN  passed  through  a  hot  tube  gives  (CN)2,  H,  N 
and  C.;  this  reaction  is  reversible  (see  Cyanogen:  Reaction  No.  3). 

2.  When  the  vapor  is  decomposed  by  electric  sparks  it  yields 
acetylene  and  nitrogen 

2HCN  r;  C2H2  +  N2  (reversible). 

An  electric  current  passed  between  platinum  electrodes, 
through  liquid  HCN,  gives  H  at  the  negative  pole,  but  no  gas  is 
evolved  at  the  positive  pole,  as  the  cyanogen  attacks  the  plati- 
num.1 

3.  Burns  (in  air  or  oxygen)  with  a  white  flame,  bordered  with 
purple.     Explodes  in  O  with  great  violence,  yielding  CO2,  H20, 
N,  and  a  little  HNO3. 

4.  Action  of  non-metals:   Sulphur  vapor  gives  the  same  pro- 
ducts as  H2S  on  CN  (see  Cyanogen:   Reaction  No.  7). 

Phosphorus  has  no  action. 

Dry  Cl  and  anhydrous  HCN  give 

HCN  +  C12  =  HC1  +  CNC1. 

Cl  and  aqueous  HCN  give  only  a  little  CNC1,  the  chief  products 
being  CO2,  CO,  HC1  and  NH3. 

Nascent  H  gives  methylamine: 

HCN  +  2H2  =  CH3  •  NH2. 

5.  Action  of  strong  acids:    Strong  HC1  and  moderately  con- 
centrated H2SO4  convert  it  into  ammonium   formate,    which  is 
decomposed  on  heating,  yielding  formic  acid: 

HCN  +  2H2O  =  H  -C02NH4. 
HCO2NH4  +  HC1  =  NH4C1  +  H  •  CO2H. 

The  gaseous  acids  (HC1,  HBr,  HI)  form  addition-compounds 
with  anhydrous  HCN,  usually  of  the  type  HX-HCN. 

Concentrated  H2SO4,  heated  in  a  closed  vessel  with  HCN  to 
30-35°  C.,  turns  brown;  SO2,  CO2,  and  N  are  given  off. 

6.  Action  of  alkalis:   At  ordinary  temperatures,  cyanides  are 
produced:  HCN  +  KOH  =  RCN 


1  Davy,  "Journ.  Science  and  Arts,"  I,  288. 


CYANOGEN  AND   ITS  COMPOUNDS   WITH   NON-METALS        55 

On  heating,  a  formate  of  the  metal  is  produced  and  ammonia 
is  evolved:  KCN  +  ^O  =  HCO2K  +  NH3. 


7.  Action  of  metallic  oxides  :  Most  metallic  oxides  yield  cyan- 
ides, in  some  cases  with  evolution  of  cyanogen. 

8.  Action  of  metallic  salts:   Hydrocyanic  acid  is  a  very  weak 
acid;   when  absolutely  pure  it  does  not  redden  litmus:   it  is  set 
free  from  its  compounds  by  almost  every  acid,  even  by  CO2. 
Alkaline  carbonates  and  most  acids  are,  however,  decomposed 
by  HCN,  the  reaction  being  to  some  extent  reversible. 

Salts  of  metals  which  give  insoluble  cyanides  are  decomposed 
by  HCN  with  precipitation  of  the  cyanide  (e.g.,  salts  of  Ag,Cu,  Pb). 
Alkaline  polysulphides  give  thiocyanates  (MCNS). 

9.  Spontaneous    decomposition:     Anhydrous    HCN    may   be 
preserved  in  sealed  vessels  without  decomposition.     If,  however, 
a  trace  of  ammonia  or   alkali  be  present,  it  decomposes,  espe- 
cially if  exposed  to  light,  turning  brown  and  yielding  ammonium 
cyanide  and  azulmic  acid,  probably  first  polymerizing  to  (HCN)3. 

Poisonous  Action  of  Hydrocyanic  Acid.  —  The  poisonous  action 
seems  to  be  chiefly  paralysis  of  the  nervous  centers.  Anything 
which  will  act  as  a  stimulus  to  the  nerves,  such  as  inhaling  chlo- 
rine or  ammonia,  will  act  as  an  antidote,  although  the  products 
of  the  reaction  in  these  cases  are  also  strong  poisons.  The  symp- 
toms produced  by  inhaling  small  quantities  of  hydrocyanic  acid 
gas  are  headache,  giddiness,  a  peculiar  sensation  at  the  back  of 
the  throat,  and  sometimes  nausea.  Long  continual  respiration 
of  small  quantities  of  hydrocyanic  acid,  as  in  some  operations  in 
the  cyanide  plant,  particularly  in  cleaning  up,  may  give  rise  to 
chronic  affections  of  the  heart  and  throat  (palpitations  and  hoarse- 
ness). The  poisonous  action  of  soluble  cyanides  is  due  to  the 
liberation  of  HCN  by  the  acids  of  the  stomach.  Various  antidotes 
have  been  proposed,  such  as  salts  of  cobalt,  hypodermic  injection 
of  peroxide  of  hydrogen,  etc.,  but  the  simplest  and  most  effective 
seems  to  be  freshly  prepared  ferrous  carbonate. 

H.  C.  Jenkens  *  recommends  the  following  solutions  to  be 
prepared  and  kept  handy  as  an  antidote  for  cases  of  cyanide 
poisoning:  (a)  A  hermetically  sealed  bottle  containing  7£  grams 
ferrous  sulphate  in  30  c.c.  of  distilled  water,  previously  well 
boiled,  (b)  A  hermetically  sealed  bottle  containing  1£  grams 

i  Trans.    I.    M.    M..    XIII.    484. 


56  THE  CYANIDE  HANDBOOK 

NaOH  in  300  c.c.  water,  (c)  A  tube  containing  2  grams  magnesia 
(MgO).  When  used,  the  sealed  ends  of  the  two  bottles  are  to  be 
broken  off  and  the  solutions  mixed,  the  magnesia  added,  and  the 
whole  administered  as  rapidly  as  possible. 

Anything  which  will  induce  vomiting  also  has  a  beneficial 
effect. 

Soluble  cyanides  introduced  into  cuts  in  the  skin  act  as  blood 
poisons,  producing  sores  and  eruptions. 

(C)     COMPOUNDS  OF  CYANOGEN  WITH  NON-METALS 

The  compounds  with  sulphur  have  been  already  mentioned. 
The  following  compounds  with  the  haloid  elements  are  known: 

CNC1  CNBr  CNI 

(CNC1)3  (CNBr)  3 

The  chloride  CNC1  is  gaseous  at  the  ordinary  temperature; 
the  others  are  solid. 

CHLORIDES  OF  CYANOGEN 
GASEOUS  CHLORIDE  (CNC1) 

Prepared:  1.  By  action  of  Cl  on  anhydrous  HCN;  the  excess 
of  Cl  is  removed  by  agitation  with  mercury. 

2.  By  action  of  Cl  on  mercuric  cyanide  (solid  or  in  saturated 
solution) :  Hg(CN)2  +  2C12  =  HgCl2  +  2CNC1. 

3.  By  passing  Cl  through  a  solution  of  KCN  surrounded  by 
a  freezing-mixture:  the  product  is  then  distilled  and  the  gaseous 
chloride  collected  and  liquefied  in  a  cooled  condenser: 

KCN  +  C12  =  KC1  +  CNC1. 

Physical  Properties.  —  Very  volatile  liquid;  boils  at  15.5°  C. 

Density  of  vapor,  20.2  (H  -  1).     Solidifies  at  -  5°  C. 

Very  poisonous;  has  extremely  irritating  odor;  produces 
coughing  and  tears.  Soluble  in  alcohol,  ether,  and  water. 

Reactions. —  1.  Polymerizes,  forming  the  solid  chloride  (CNC1)3 
in  presence  of  a  slight  excess  of  Cl. 

2.  Decomposed  when  heated  with  certain  metals,  yielding  a 
cyanide  or  cyanogen: 

CyCl  +  2K  =  KC1  +  KCy. 
3CyCl  +  Sb  =  SbCl3  +  3Cy. 


CYANOGEN  AND   ITS  COMPOUNDS   WITH   NON-METALS        57 

3.  Decomposed  by  water  in  two  stages: 

CNC1  +  H2O  =  HC1  +  HCNO. 
HCNO  +  HC1  +  H2O  =  NH4C1  +  CO2. 

4.  Alkalis  give  an  analogous  reaction: 

CNC1  +  2KOH  =  KC1  +  KCNO  +  H2O 
KCNO  +  2HC1  +  H2O  =  KC1  +  NH4C1  +  CO2. 

5.  Dry  ammonia  gas  forms  ammonium  chloride  and  cyan- 
amide: 


CNC1  +  2NH3  =  NH4C1  +  CN  .NH2 
6.    Does  not  precipitate  AgCl  or  AgCN  from  silver  nitrate. 

SOLID  CHLORIDE  (CNC1)3 

Preparation.  —  1  .  By  exposing  to  sunlight  a  mixture  of  chlorine 
with  excess  of  Hg(CN)2  in  sealed  tubes: 

3Hg(CN)2  +  6C12  =  3HgCl2  +  2(CNC1)3. 

2.  By  action  of  phosphorus  pentachloride  on  cyanuric  acid: 

(CNOH)3  +  3PC15  =  3POC13  +  3HC1  +  (CNC1)8. 

3.  By  slightly  heating  dry  KCNS  in  a  current  of  dry  chlorine: 

3KCNS  +  6C12  =  3KC1  +  3SC12  +  (CNC1)8. 
The  (CNC1)3  crystallizes  from  the  mixture. 

Physical  Properties.  —  Small  needles  (density  1.32),  melting 
at  140°  C.  to  a  transparent  liquid  which  boils  at  190°  C. 

Vapor  density,  6.35  (air  =  1).  Very  poisonous.  Easily  pro- 
vokes tears.  Smells  of  chlorine,  but  also  has  an  odor  suggestive 
of  mice. 

Reactions.  —  1.  Decomposed  by  water  (more  rapidly  by  alkalis), 
forming  a  cyanurate: 

(CNC1).  +  3H20  =  3HC1  +  (CNOH)3. 
2.    Ammonia  gives  chlorocyanuramide: 
(CN)3(NH2)2-C1. 

BROMIDES  OF  CYANOGEN 
MONOBROMIDE  (CNBr) 

Preparation.  —  1.  By  adding  a  strong  solution  of  KCN  grad- 
ually to  an  excess  of  bromine  until  the  latter  is  discolored,  then 
distilling  and  condensing  the  product 

KCN  +  Br2  =  KBr  +  CNBr. 


58  THE  CYANIDE  HANDBOOK 

2.  By  acting  upon  sodium  bromide  and  bromate  with  sodium 
cyanide  and  sulphuric  acid  at  70°  C.     (Gopner.)1 

2NaBr  +  NaBrO3  +  3NaCN  +  3H2SO4  =  3Na2SO4  +  3H2O  +  SCNBr. 

3.  By  adding  bromine  drop  by  drop  to  a  solution  of  HCN: 

HCN  +  Br2  =  HBr  +  CNBr. 

When  Br  is  added  to  an  excess  of  cyanide  (reversing  the  order 
of  procedure  in  the  first  method),  there  is  a  tendency  to  formation 
of  the  polymer  (CNBr)3. 

4.  One  part  of  Br  is  added  gradually  to  two  parts  mercuric 
cyanide:  Hg(CN)2  +  2Br2  =  HgBr2  +  2CNBr. 

The  same  reaction  may  be  brought  about  by  adding  a  mixture 
of  mercuric  cyanide  and  hydrochloric  acid  to  bromine  in  a  cooled 
vessel,  and  then  distilling  off  the  CNBr  by  placing  the  vessel  in 
hot  water. 

Physical  Properties.  —  A  transparent  crystalline  solid,  said  to 
melt  at  4°  —  12°  C.;  at  ordinary  pressures,  however,  it  volatizes 
without  melting  and  is  gaseous  above  61°  C.  It  is  volatile  above 
15°  C.  It  has  a  very  penetrating  odor,  attacking  the  eyes  and 
causing  a  flow  of  tears. 

Very  poisonous,  but  less  so  than  HCN.  Very  soluble  in 
water  and  alcohol.  With  water  it  forms  a  hydrate  which  is  less 
volatile  than  the  pure  bromide  of  cyanogen.  Solution  bleaches 
litmus  without  reddening  it.  Crystallizes  in  long  hexagonal 
needles,  which  soon  change  to  cubic  or  tabular  crystals.2 

Reactions.  —  1.  Gradually  decomposed  by  water  with  forma- 
tion of  cyanic  acid  and  hydrobromic  acid: 

CNBr  +  H2O  =  HCNO  +  HBr. 

When  an  aqueous  solution  of  CNBr  is  evaporated  to  dryness, 
ammonium  bromide  is  obtained  and  carbon  dioxide  evolved: 
CNBr  +  2H2O  =  NH4Br  +  CO2. 

2.  Decomposed  rapidly  by  alkalis,  with  formation  of  a    bro- 
mide and  cyanate: 

CNBr  +  2KOH  =  KBr  +  KCNO  +  H2O. 

3.  Acids  (H2SO4,  HC1,  HNO3)  dissolve  it  without   decomposi- 
tion, but  S02  is  oxidized  by  CNBr  in  presence  of  water: 

CNBr  +  SO2  +  2H2O  =  HBr  +  H2SO4  +  HCN. 

1  See  "Journ.  Soc.  Chem.  Ind.,"  XXV,  1130. 

2  H.  L.  Sulman,  "Proc.  Chem.  Met.  and  Min.  Soc.  of  South  Africa,"  I,  114. 


CYANOGEN   AND   ITS  COMPOUNDS   WITH   NON-METALS        59 

4.   Soluble  cyanides  act  rapidly,  probably  evolving  cyanogen 
as  follows:  KCN  +  CNBr  =  KBr  +  (CN)a> 

It  is  possible,  however,  that  hydrocyanic  acid  is  evolved,  as 
ollows:        CNBr  +  2KCN  +  H20  =  KCNO  +  KBr  +  2HCN 


The  liberation  of  cyanogen  in  an  active  form  appears  to  be 
the  cause  of  the  rapid  solvent  power  on  gold  of  the  mixture  of 
KCN  and  CNBr. 

5.  Action  on  Metals.  —  Certain  metals  are  attacked,  giving  a 
metallic  bromide  with  evolution  of  cyanogen: 

Hg  +  2CNBr  =  HgBr2  +  (CN)2  (in  solution). 
A  similar  reaction  occurs  with  the  vapor  of  antimony. 
Gold  and  silver  are  rapidly  dissolved  by  a  mixture  of  CNBr 
and  an  alkali  cyanide,  forming  the  soluble  double  cyanides: 

3KCN  +  CNBr  +  2Au  =  2KAu(CN)2  +  KBr. 
3KCN  +  CNBr  +  2Ag  =  2KAg(CN)2  +  KBr. 

This  represents  the  final  effect  of  the  reaction,  but  it  may  take 
place  in  several  stages.  Bromide  of  cyanogen  alone  does  not 
attack  gold  or  silver. 

6.  Ammonia  decomposes  cyanogen  bromide,  giving  bromide 
and  cyanate  of  ammonium: 

CNBr  +  2NH3  +  H2O  =  NH4Br  +  NH4CNO. 

POLYMER  OF  CYANOGEN  BROMIDE  (CNBr)3 

This  substance  is  sometimes  obtained  during  the  preparation 
of  ordinary  cyanogen  bromide.  It  is  formed  by  heating  CNBr 
for  5  to  6  hours  at  130°-140°  in  sealed  tubes,  but  is  partially  decom- 
posed with  liberation  of  bromine.  It  is  obtained  in  a  purer  con- 
dition by  heating  CNBr  with  anhydrous  ether. 

This  is  a  solid  body,  melting  at  300°  C.,  and  boiling,  with 
decomposition,  at  a  higher  temperature.  It  is  insoluble  in  alco- 
hol and  nearly  insoluble  in  ether. 

Exposed  to  moist  air,  or  heated  with  water  to  100°  in  sealed 
tubes,  it  forms  cyanuric  acid: 

(CNBr)3  +  3H2O  =  (CNOH)3  +  3HBr. 
IODIDE  OF  CYANOGEN  (CNI) 

Preparation.  —  1.  Not  formed  by  direct  union  of  the  ele- 
ments. 


60  THE  CYANIDE  HANDBOOK 

2.  Formed  by  action  of  free  iodine  on  the  cyanides  of  mercury, 
silver,  or  potassium: 

Hg(CN)2  +  2I2  =  2CNI  +  HgI2. 
KCN  +  I2  =  CNI  +  KI. 

The  iodide  of  cyanogen  is  separated  from  the  mixture  by  dis- 
tilling at  a  temperature  below  135°  C. 

Physical  Properties.  —  Forms  long  needles,  soluble  in  water, 
alcohol  or  ether.  Crystallizes  from  these  solutions  in  four-sided 
tables.  Volatile  at  ordinary  temperatures  and  boils  below  100° 
C.  Has  a  penetrating  odor  resembling  CN  and  I.  Poisonous. 
Does  not  redden  litmus. 

Reactions.  —  1.  Decomposed  by  heat,  on  passing  through  a 
red-hot  tube:  2CNI  =  (CN)z  +  Iz 

2.  Gradually  decomposed  by  water: 

CNI  +  H2O  =  HCNO  +  HI. 

3.  Dissolved  by  alkalis  with  formation  of  a  cyanide  and  an 
iodate,  a  little  cyanate  being  formed  at  the  same  time: 

6KOH  +  3CNI  =  3KCN  +  KIO3  +  2KI  +  3H2O. 

2KOH  +  CNI  =  KCNO  +  KI  +  H2O. 
(Note  difference  from  CNBr.) 

4.  Action  of  Acids.  —  HC1  and  H2SO4  slowly  decompose  it 
with  liberation  of  HCN  and  I  at  ordinary  temperatures. 

Sulphurous  acid  acts  as  follows: 

CNI  +  SO2  +  2H2O  =  HI  +  H2SO4  +  HCN. 

5.  Soluble  cyanides  react  as  with  CNBr,  but  less  vigorously. 
The  action  on  metals  is  also  similar. 

6.  Action  of  Non-metals.  —  Chlorine  does  not  decompose  dry 
CNI. 

Phosphorus  has  a  violent  action,  often  accompanied  by  light; 
iodide  of  phosphorus  is  formed  and  cyanogen  probably  liberated. 
(Phosphorus  has  only  a  slight  action  on  CNBr.) 

7.  Dry  H2S  gives: 

2CNI  +  H2S  =  SI2  +  2HCN. 
In  presence  of  water,  the  reaction  is: 

CNI  +  H2S  =  S  +  HI  +  HCN 

8.  Ammonia  is  slowly  absorbed,  giving  ammonium  iodide  and 
cyanamide:  CNI 


CYANOGEN  AND  ITS   COMPOUNDS   WITH  NON-METALS        61 

9.  Solution  of  CNI  in  water  gives  no  precipitate  with  solutions 
of  silver  salts. 

10.  On  mixing,  in  the  following  order,  solutions  of  CNI,  KOH, 
FeSO4  and  HC1,  a  green  precipitate  is  obtained.     This  reaction 
does  not  occur  with  CNC1  or  CNBr,  unless  the  FeSO4  be  added 
before  the  KOH. 


SECTION   II 

SIMPLE   METALLIC  CYANIDES 
(INCLUDING  THE  EASILY-DECOMPOSED  DOUBLE  CYANIDES) 

WE  shall  now  consider  those  metallic  compounds  in  which 
the  group  CN  occurs  as  the  negative  radical.  This  includes  all 
the  substances  which  can  correctly  be  described  as  metallic  cyan- 
ides. Compounds  such  as  ferrocyanides,  nitroprussides,  thio- 
cyanates,  etc.,  have  little  in  common  with  the  true  cyanides,  and 
are  more  conveniently  considered  as  compounds  of  entirely  dis- 
tinct radicals,  Fe(CN)6,  Fe(CN)5NO,  (SCN),  etc. 

The  true  cyanides  have  the  general  formula 

/CN 

m'  —  C  =  N,  m"  <5!?l  m'"r-CN,  etc. 
\CN         \CN 

where  m',  m",  etc.,  are  positive  monad,  dyad,  etc.,  elements  or 
radicals.  They  show,  however,  a  great  tendency  to  combine 
with  each  other,  forming  compounds  of  the  type 

miCN  •  m2CN,  possibly  mi  —  C  =  N. 
ma  —  C  =  N. 

where  n\l  and  m2  are  different  positive  radicals. 

It  is  also  possible  that  isomeric  modifications  exist  in  which 
the  positive  radical  is  united  directly  with  carbon  or  nitrogen: 
m  —  C  =  N'"  orm  — Nv  =  C. 

corresponding  with  the  organic  groups  known  as  nitriles  and  car- 
bamides. 

General  Modes  of  Formation.  —  1.  By  direct  action  of  cyan- 
ogen on  metals:  (CN)JJ  +  2R  =  2RCN 

2.  By  action  of  cyanogen  on  dissolved  alkalis  with  simulta- 
neous formation  of  a  cyanate: 

(CN)2  +  2KOH  =  KCN  +  KCNO  +  H2O. 
62 


SIMPLE  METALLIC  CYANIDES  63 

3.  By  action  of  hydrocyanic  acid  on  metals,  oxides,  or  metallic 
salts. 

4.  By   double   decomposition,   with   metallic   salt   and  other 
cyanides:  MjCN  +  MjiX  =  M]X 


where  M1?  M2  are  two  different  metallic  radicals  and  X  a  negative 
(acid)  radical. 

5.  By  calcination  of  nitrogenous  organic  matter  at  a  high 
temperature  with  alkalis  or  alkaline  carbonates. 

6.  By  passing  free  nitrogen  over  a  mixture  of  carbon  and  an 
alkaline  carbonate  heated  to  redness. 

7.  By  calcining  certain  organic  salts  such  as  acetates  and 
tartrates,  with  the  nitrates  or  nitrites  of  the  alkalis. 

General  Properties.  —  Cyanides  of  the  alkalis  and  alkaline 
earths  are  soluble  in  water;  the  simple  cyanides  of  mercury  and 
cadmium  are  also  soluble;  other  simple  cyanides  are  insoluble. 
Many  of  the  insoluble  cyanides  unite  with  alkaline  or  other  soluble 
cyanides  to  form  soluble  double  salts. 

Soluble  compounds  are  also  formed  with  ammonium  salts,  and 
with  certain  other  metallic  salts. 

Most  soluble  cyanides  have  an  alkaline  reaction  and  are  very 
poisonous. 

The  soluble  cyanides  are  colorless.  The  insoluble  cyanides 
often  have  characteristic  colors. 

General  Reactions.  —  1.  Action  of  heat:  The  alkali  cyanides, 
when  anhydrous,  are  not  decomposed  by  ordinary  heat.  KCN 
and  NaCN  may  be  fused  without  decomposition.  Hydrated  NaCN 
is  partially  decomposed  with  evolution  of  NH3.  Of  the  cyanides 
of  the  alkaline  earths,  BaCy2  is  the  most  stable  and  MgCy2  the 
least.  The  former  may  be  heated  to  redness  without  decomposi- 
tion. Some  cyanides  (Zn,  Cu)  are  decomposed  by  heat  into  a 
mixture  of  C  with  the  metal  or  a  metallic  carbide,  N  being  given 
off;  others  (Hg,  Ag)  are  decomposed  into  metal  and  CN. 

2.  Action  of  Oxygen.  —  Alkaline  cyanides  are  converted  into 
cyanates,  and  by  stronger  heating  into  carbonates  with  evolution 
of  N.      The  reaction  takes  place  more  readily  in  presence  of  an 
oxidizing  agent.     With  other  cyanides,  CO2  and  N  are  given  off, 
and  an  oxide  of  the  metal  remains.     Cyanides  explode  in  contact 
with  certain  oxidizing  bodies  (nitrates,  chlorates). 

3.  Action  of  Chlorine.  —  Varies  under  different  conditions.     In 


64  THE  CYANIDE  HANDBOOK 

general  a  chloride  is  formed,  with  free  CN  and  more  or  less  CNC1. 
Bromine  and  iodine  act  similarly. 

4.  Action  of  Water.  —  Decomposes  all  cyanides  at  a  higher  or 
lower   temperature,   generally   at    100°   C.     Boiling   solutions   of 
alkaline  cyanides  are  converted  into  alkaline  formates  with  evolu- 
tion of  ammonia: 

mCN  +  2H2O  =  HCO2m  +  NH3. 

Cyanides  of  the  heavy  metals,  heated  in  presence  of  water, 
decompose,  yielding  CO2,  CO,  HCN,  NH3,  the  metal  remaining  as 
oxide,  or  in  the  free  state  mixed  with  a  little  carbon. 

Cyanides  of  Hg  and  Ag,  heated  with  water  in  sealed  tubes  to 
280°  C.,  give  ammonium  carbonate  and  the  free  metal.1 

5.  Action  of  Acids.  —  Dilute  mineral  acids  decompose  most 
metallic  cyanides  with  evolution  of  HCN.     Many  organic  acids 
also  decompose  cyanides.     Weak  acids,  such  as  CO2,  decompose 
the  cyanides  of  the  alkalis  and  alkaline  earths,  and  some  double 
cyanides.     The  cyanides  of  Hg,  Ag,  and  Pd  are  not  decomposed 
by  dilute  HC1,  but  on  the  contrary  HCN  displaces  HC1  in  the 
chlorides  of  these  metals.     Nitric  acid  decomposes  cyanides  with 
liberation  of  N  and  C02  and  formation  of  oxalic  acid.     Concen- 
trated H2SO4  gives  a  sulphate  of  the  metal,  and  of  ammonium, 
and  forms  CO. 

6.  Mercuric  oxide  decomposes  most  cyanides,  when  boiled 
with  their  solution,  giving  mercuric  cyanide  (HgCy2)  and  the 
corresponding  oxide.  This  reaction  is  owing  to  the  great  stability 
of  mercuric  cyanide.1 

DETAILS  RESPECTING  CERTAIN  METALLIC  CYANIDES 

Ammonium  Cyanide  (NH4CN) :  Preparation.  —  1.  By  heat- 
ing ammonium  ferrocyanide  and  condensing  the  product  in  a 
cooled  receiver: 

(NH4)4  FeCy6  =  FeCy2  +  4NH4Cy. 

2.  By  heating  ammonium  salts  with  certain  cyanides  or  ferro- 
cyanides,  e.g.: 

K4FeCy6  +  4NH4C1  =  4NH4Cy  +  4KC1  +  FeCy2. 
HgCy2  +  2NH4C1  =  HgCl2  +  2NH4Cy. 

3.  By  direct  union  of  NH3  gas  and  HCN. 

i  It  is  probable  that  most  cyanides  are  ionized  in  dilute  solution.  With  mer- 
curic cyanide,  however,  this  is  not  the  case. 


SIMPLE  METALLIC  CYANIDES  65 

4.    By  passing  NH3  over  red-hot  carbon: 

2NH3  +  C  =  NH4CN  +  H2. 
also 

2NH3  +  CO  =  NH4CN  +  H2O. 

It  is  also  one  of  the  products  of  combustion  of  illuminating 
gas  containing  ammoniacal  vapors,  and  is  formed  by  action  of 
HNO3  on  some  organic  substances. 

Physical  Properties.  —  Crystallizes  in  cubes.  Very  volatile  and 
poisonous.  Boils  about  36°  C.,  and  is  easily  dissociated  into 
HCN  and  NH3.  Vapor  density  at  100°  C.  0.79  (air  =  1). 

Reactions.  —  1.  Burns  in  air  or  oxygen,  giving  a  yellowish 
flame,  depositing  ammonium  carbonate. 

2.  Very  unstable,  particularly  at  high  temperatures.     Turns 
brown  and  passes  into  azulmic  acid. 

3.  Decomposed  by  chlorine  or  bromine: 

NH4Cy  +  C12  =  CyCl  +  NH4C1. 

CYANIDES  OF  ALKALI  METALS 

Potassium    Cyanide    (KCN) :     Preparation    (methods    mostly 
applicable  also  to  sodium   cyanide).  —  1.   By   direct   action   of 
hydrocyanic  acid  on  potash  (best  in  alcoholic  solution) : 
HCN  +  KOH  =  H2O  +  KCN. 

2.  By    decomposition    of   ferrocy anide :     (a)    By   heating   in 
closed  vessels;    (b)    by  heating  with  dry  potassium  carbonate; 
(c)    by  action  of  metallic  sodium  (giving  a  mixture  of  NaCy  and 
KCy).     These  methods  will  be  discussed  in  detail  under  the  title 
"Manufacture  of  Cyanide." 

(a)  The  effect  of  heating  K4FeCy6  by  itself  in  a  closed  vessel 
is  to  partially  break  it  up  into  N  and  a  carbide  of  iron,  mixed  with 
KCN. 

(b)  When  heated  with  K2CO3: 

K4FeCy6  +  KzCOa  =  5KCy  +  KCyO  +  CO2  +  Fe. 

Similar  reaction  with  Prussian  bhie  and  K2CO3. 

(c)  With  metallic  sodium: 

K4FeCye  +  Na2  =  2NaCy  +  4KCy  +  Fe. 

3.  By  calcining  nitrogenous  organic  matter  with  K2CO3.     A 
part  of  the  carbon  liberated  reduces  K2CO3  to  K,  which  then 
reacts  with  N  and  more  C  to  form  KCN. 


66  THE  CYANIDE  HANDBOOK 

4.  By  passing  atmospheric  nitrogen  over  a  mixture  of  carbon 
and  potash  heated  to  redness: 

Nz  +  4C+  K2CO3  =  2KCN  +  3CO. 

or 

N2  +  3C  +  2KOH  =  2KCN  +  CO  +  H2O. 

Probably  K  is  first  liberated  in  this  case  also. 

5.  By   precipitating   mercuric    cyanide   with   potassium   sul- 

Phide:  HgCy2  +  K2S  =  HgS  +  2KCy. 

0  Physical  Properties.  —  Anhydrous.  Crystallizes  in  cubic  sys- 

.\  tern  by  fusion  and  in  cubic  octahedra  from  aqueous  solutions. 
\  Deliquescent;  —  readily  soluble  in  water;  insoluble  in  absolute 

alcohol.  Strongly  alkaline  taste  and  reaction.  Very  poisonous. 
Gives  off  HCN  when  exposed  to  air.  Melts  at  red  heat  and  volatil- 
izes at  a  white  heat  without  decomposition. 

Reactions.  —  1.  When  heated  in  contact  with  air  a  little 
KCNO  is  always  formed.  When  heated  with  metallic  oxides, 
such  as  those  of  Pb,  Sb,  Fe,  As,  Sn,  or  Mn  (MnO2),  larger  quanti- 
ties of  cyanate  are  produced,  and  the  oxide  is  reduced  to  metal, 
or,  in  the  case  of  MnO2,  to  MnO.  When  heated  with  oxidizing 
agents  (nitrates  or  chlorates)  it  explodes  violently. 

KMnO4  gives  as  oxidation  products  CO2,  HCO2H,(CO2H)2, 
CO(NH2)2,  HNO2  and  NH3. 

Chloride  of  lime  gives  calcium  cyanate. 

Potassium  sulphate  gives  cyanate  and  sulphide: 

K2SO4  +  4KCN  =  4KCNO  +  KaS. 

2.  The  aqueous  solution  decomposes  even  at  ordinary  temper- 
ature, giving  potassium  formate  and  ammonia,  but  much  more 
rapidly  on  boiling: 

KCN  +  2H2O  =  HCO2K  +  NH3. 

3.  On  electrolysis  it  gives  CO2,  NH3  and  KOH. 

4.  When  melted  with  sulphur  it  forms  a  thiocyanate: 

KCN  +  S  =  KSCN. 

Aqueous  solution  of  KCN  does  not  dissolve  sulphur,  but  poly- 
sulphides  react  with  KCN  in  solution  as  follows: 
2KCN  +  K^Ss  =  2KCNS  +  KaS. 

Selenium  reacts  in  a  similar  way,  but  also  dissolves  in  KCN 
solution,  even  at  ordinary  temperature,  to  form  seleno  cyanide  — • 


SIMPLE  METALLIC  CYANIDES  67 

KSeCN  (soluble  in  water  to  a  colorless  solution).     When  fused 
with  tellurium  it  forms  potassium  telluride  (giving  a  pink  solution) : 

2KCN  +  Te  =  K2Te  +  (ON),. 

5.  Sulphureted  hydrogen  passed  into  a  solution  of  KCN  gives 
small  yellow  needles  of  "  chrysean  "  and  potassium  and  ammonium 
sulphides  in  solution: 

4KCN  +  5H2S  =  2K2S  +  NH4HS  +  CJIsNaSa. 

6.  On  heating  with  alkalis,  it  is  transformed  first  into  HCO2K 
and  NH3;  but  on  heating  to  redness  H  is  evolved  and  an  alkaline 
carbonate  remains. 

7.  Thiosulphates  convert  it  into  thiocyanate: 

KaSaO,  +  KCN  =  K.S03  +  KCNS. 

8.  The  reactions  with  Cl,  Br  and  I' are  given  under  Section 
I  (c). 

9.  Certain  metals  are  dissolved  in  aqueous  solution  of  potas- 
sium cyanide: 

(a)  In  presence  of  oxygen: 

2Au  +  4KCy  +  O  +  H2O  =  2KAuCy2  +  2KOH. 
2Ag  +  4KCy  +  O  +  H2O  =  2KAgCy2  +  2KOH. 

(b)  With  evolution  of  hydrogen: 

Zn  +  4KCy  +  2H2O  =  K2ZnCy4  +  2KOH  +  H2. 
(also  with  Cu,  Fe  and  Ni). 

(c)  The  following  are  insoluble:   Pt,  Hg,  Sn.     (Hg,  however, 
dissolves  to  some  extent,  under  the  conditions  of  cyanide  treat- 
ment, from  amalgamated  plates  in  the  battery.) 

10.  Many  metallic  oxides  dissolve  to  form  the  corresponding 
cyanide,  or  double  cyanide  of  the  metal  and  potassium. 

Sodium  Cyanide  (NaCN) :  Formation  (see  under  "  Potassium 
Cyanide,"  above).  —  1.  By.  passing  a  current  of  anhydrous  HCN 
into  alcoholic  solution  of  caustic  soda.  Sodium  cyanide  is  pre- 
cipitated in  the  anhydrous  form,  and  must  be  rapidly  washed 
with  alcohol  and  dried. 

2.  When  ammonia  is  passed  over  a  heated  mixture  of  metallic 
sodium,  or  sodium  carbonate  and  carbon,  it  forms  sodium  cyanide, 
with  sodium  cyanamide  as  intermediate  product: 

Na2  +  C  +  2NH3  -  Na2CN2  +  3H2. 
Na2CN2  +  C  -  2NaCN. 


68  THE  CYANIDE  HANDBOOK 

3.  By  fusing  barium  cyanide  with  sodium  carbonate: 

BaCy2  +  Na2CO3  =  BaCO3  +  2NaCy. 

The  sodium  cyanide  is  separated  from  the  insoluble  BaCO3  by 
extracting  with  water. 

4.  By  fixation  of  atmospheric  nitrogen,  using  the  following 
series  of  reactions: 

CaO  +  2C"+  2N  =  CaCN2  +  CO  (in  electric  furnace). 

2CaCN2  +  4H2O  =  (CN  •  NH2)2  +  2Ca(OH)2. 
(CNNH2)2  +  Na,CO3  +  2C  =  2NaCN  +  NH3  +  SCO  +  H  +  N 

(These  processes  will  be  more  fully  discussed  under  "Manu- 
facture of  Cyanide. ") 

Properties.  —  Sodium  cyanide  is  a  white  crystalline  solid, 
similar  in  general  appearance  and  properties  to  potassium  cyanide. 
It  is  very  deliquescent,  and  forms  two  hydrates,  of  the  composi- 
tion, NaCN  •  2H2O  and  2NaCN  •  H2O,  respectively.  The  first  is 
white,  crystallizing  in  thin  plates,  the  second  yellowish.  Both 
these  hydrates  are  unstable,  and  give  off  ammonia,  even  when 
protected  from  the  air,  at  the  ordinary  temperature. 

Reactions.  —  Analogous  to  those  of  potassium  cyanide.  Cer- 
tain alleged  differences  in  the  behavior  of  the  two  cyanides  in 
the  treatment  of  ores  will  be  discussed  later. 

CYANIDES  OF  THE  ALKALINE  EARTH  METALS 

Barium  Cyanide  (Ba(CN)2):  Preparation. —  1.  By  calcination 
of  Ba2Fe(CN)6. 

2.  By  passing  anhydrous  HCN  over  Ba(OH)2. 

3.  By  passing  a  current  of  air  over  a  mixture  of  BaO  and 
carbon  at  a  high  temperature,  or,  better,  by  passing  air  previously 
freed  from  oxygen  and  water  vapor  over  a  heated  mixture  of  BaCO3 
and  charcoal,  tar,  or  other  carbonaceous  matter. 

Barium  carbide  (BaC2)  is  first  formed,  which  combines  with 
nitrogen,  giving  Ba(CN)2. 

Properties.  —  White,  anhydrous,  or  crystallizing  as  BaCy2- 
2H2O.  Loses  water  in  vacuo  at  ordinary  temperature,  forming 
BaCy2  •  H2O.  Very  soluble  and  deliquescent.  Completely  dehy- 
drated by  heating  in  a  current  of  dry  air  at  75°  and  then  at  100°  C. 

Reactions.  —  1.    Decomposes  on  heating: 

Ba(CN)2  +  3H2O  =  BaCO3  +  NH3  +  HCN  +  H2. 
Ba(CN)2  +  2H20  =  BaO  +  CO  +  NH3  +  HCN. 


SIMPLE  METALLIC  CYANIDES  69 

2.  Decomposed  by  carbon  dioxide: 

Ba(CN)2  +  CO2  +  H2O  =  2HCN  +  BaCO3. 

3.  Fused  with  alkaline  carbonates  it  yields  BaCO3  and  the 
corresponding  alkaline  cyanide. 

Strontium  Cyanide  (Sr(CN)2).  —  Analogous  in  preparation  and 
properties  to  the  above.  Crystallizes  as  SrCy2  .  4H2O.  Less  stable 
than  BaCy2;  more  so  than  CaCy2. 

Calcium  Cyanide  (Ca(CN)2):  Preparation.  —  1.  By  action  of 
HCN  on  lime. 

2.  By  passing  nitrogen  over  calcium  carbide,  the  chief  product 
is  calcium  cyanamide: 

CaC2  +  N2  =  CaCN2  +  C  (at  800°  C.). 

When  this  is  heated  to  a  higher  temperature  (preferably  with 
addition  of  salt  to  facilitate  the  reaction)  it  is  decomposed  as 

follows:  CaCN2  +  C  =  Ca(CN)2 

Physical  properties.  —  Said  to  have  been  obtained  in  anhy- 
drous cubes,  but  very  unstable. 

Reactions.  —  1.  Dilute  solutions  are  tolerably  stable,  but  a 
concentrated  solution  placed  in  vacuo  gradually  decomposes, 
blackens,  and  gives  the  ordinary  products  of  decomposition  of 
HCN.  In  presence  of  dehydrating  agents  and  KOH,  small  crys- 
talline needles  of  the  oxycyanide,  6CaOCaCy2-15H2O,  are  formed. 

2.   Concentrated  alcohol  gives  a  precipitate  of  calcium  hydrate. 

Magnesium  Cyanide  (Mg(CN)2)  [existence  doubtful]  :  Prepara- 
tion. —  1.  By  dissolving  freshly  precipitated  Mg(OH)2  in  HCN 
(Scheele). 

2.   By  passing  CO  or  CO2  over  heated  magnesium  nitride: 

Mg3N2. 

Properties.  —  Very  unstable.  Solution  decomposes  on  evap- 
oration, liberating  HCN  and  leaving  Mg(OH)2.  Decomposed  by 
CO2  with  precipitation  of  MgCO3. 

Magnesium  salts  decompose  alkaline  cyanides  thus: 

MgSO4  +  2KCN  +  2H2O  =  KaSC^  +  Mg(OH)2  +  2HCN. 


CYANIDES  AND  DOUBLE  CYANIDES  OF  ZINC 

Zinc  Cyanide  (Zn(CN)2):  Preparation.  —  1.    By  precipitating 
a  salt  of  zinc  with  an  alkaline  cyanide  in  suitable  proportions: 
2KCy  +  ZnSO4  =  K£O4  +  ZnCy2. 


70  THE  CYANIDE  HANDBOOK 

2.  By  the  action  of  HCN  on  the  oxide  or  acetate  of  zinc. 
These  reactions  are  incomplete  and  appear  to  be  reversible: 

Zn(CH3C02)2  +  2HCN  ^  2CHsCO2H  +  Zn(CN)2. 
ZnO  +  2HCN  ^  H2O  +  Zn(CN)2. 

Properties.  —  White,  amorphous  or  crystallized  in  orthorhom- 
bic  prisms.  Insoluble  in  water.  Unalterable  when  dry. 

Reactions.  —  1.  Heated  in  a  closed  vessel,  gives  a  black  car- 
bonaceous residue. 

2.  Dissolves  in  alkalis,  forming  a  double  cyanide  and  zincate: 
2ZhCy2  +  4KOH  =  K2ZnCy4  +  Zn(OK)2  +  2H2O. 

probably  in  two  stages: 

'(a)    ZnCy2  +  2KOH  =  2KCy  +  Zn(OH)2 

(6)  ZnCy2  +  Zn(OH)2  +  2KCy  +  2KOH  =  K2ZnCy4  + 
Zn(OK)2  +  2H2O. 

3.  Dissolves  in   alkaline  cyanides,   forming  double   cyanides 
(ZnCy2  •  2mCy) : 

ZnCy2  +  2mCy  =  m2ZnCy4  [m  =  K,  Na,  NH4]. 

Zinc-Potassium  Cyanide  (K2Zn(CN)4):  Preparation.  —  1.  By 
dissolving  ZnCy2  in  excess  of  KCy  (see  above). 

2.  By  acting  on  metallic  zinc  with  KCy  in  excess: 

Zn  +  4KCy  +  2H2O  -  K2ZnCy4  +  2KOH  +  H2. 

3.  By  dissolving  ZnO  or  ZnCO3  in  a  mixture  of  KCy  and  HCy: 

ZnCO3  +  2KCy  +  2HCy  =  K2ZnCy4  +  H2O  +  CO2. 

Properties.  —  Regular  transparent  colorless  octahedra.  Can  be 
fused  without  decomposition.  Very  soluble  in  water  at  all  tem- 
peratures. 

Reactions.  • —  1.  Decomposed  by  dilute  acids,  first  with  pre- 
cipitation of  ZnCy2,  which  is  further  decomposed  by  excess  of 

acicl :  K2ZnCy4  +  2HC1  -  ZnCy2  +  2HCy  +  2KC1. 

ZnCy2  +  2HC1  =  ZnCl2  +  2HCy. 

2.  Gives  precipitates  of  insoluble  double  cyanides  of  zinc  with 
various  solutions  of  metallic  salts  (e.g.,  those  of  Ba;  Ca,  Ni,  Co, 
Al,  Fe,  Hg,  Cu,  Pb). 

3.  With  silver  nitrate  it  gives  first  a  precipitate  of  ZnCy2, 
and  on  adding  excess  of  AgNO3  this  is  decomposed,  giving  AgCy: 

K2ZnCy4  +  AgNO3  -  ZnCy2  +  KAgCy2  +  KNO3. 

ZnCy2  +  2AgNO3  =  2AgCy  +  Zn(NO3)2 
1  This  reaction  is  discussed  in  detail  in  Section  V. 


SIMPLE   METALLIC  CYANIDES  71 

Other  Double  Cyanides  of  Zinc.  —  The  double  cyanides  of 
zinc,  with  NH4,  Na,  K,  and  Ca,  are  soluble  in  water;  the  remainder 
are  more  of  less  insoluble. 

The  double  cyanide  of  Zn  and  ammonium  is  unstable,  and 
decomposes  in  solution: 

(NH4)2ZnCy4  ±^  ZnCy2  +  2NH4Cy. 

CYANIDES  OF  THE  IRON  GROUP 

The  simple  cyanides  of  iron,  manganese,  nickel,  and  cobalt  are 
unstable;  the  chromic  cyanide  is  tolerably  stable.  No  simple 
cyanide  of  aluminium  is  known.  All  these  compounds  show  a 
great  tendency  to  form  double  salts  by  reacting  with  alkaline 
cyanides. 

The  double  cyanides  of  nickel  are  easily  decomposable,  and 
are  more  or  less  analogous  to  those  of  zinc;  they  are  of  the 
general  type  NiCy2  •  2mCy,  and  are  decomposed  by  dilute  acids  in 
the  same  way.  Thus: 

2HC1  +  NiCy22KCy  =  NiCy2  +  2KC1  +  2HCy. 
NiCy2  +  2HC1 .  =  NiCl2  +  2HCy. 

The  remainder  form  characteristic  compounds  of  complex 
cyanogen  radicals,  which  are  not  decomposed  by  dilute  acids, 
and  will  be  described  later. 

The  characteristic  colors  of  the  simple  cyanides  of  this  class 
are  as  follows: 

Iron  (ferrous) Reddish  yellow. 

"    (ferric) Deep  brown (  solution  only). 

Manganese  (manganous) White,  turning  brown. 

Nickel Apple  green. 

Cobalt    Pink. 

Chromium  (chromous) White. 

(chromic)      Grayish  blue. 

CYANIDES  OF  THE  PRECIOUS  METALS 

Cyanides  of  Gold.  —  Gold  forms  two  simple  cyanides:  Aurous 
cyanide  (AuCN)  and  Auric  cyanide  (Au(CN)3).  It  also  forms 
two  corresponding  classes  of  double  cyanides:  Aurous  (mAu(CN)2) 
and  Auric  (mAu(CN)4). 


72  THE  CYANIDE  HANDBOOK 

Aurous  cyanide  (AuCN) :  Preparation.  —  1.  By  decomposing 
auro-potassic  cyanide  with  acids: 

KAuCy2  +  HC1  =  AuCy  +  HCy  +  KC1. 

The  mixture  remains  clear  at  ordinary  temperatures,  but  becomes 
turbid  and  deposits  AuCy  at  50°  C. 

2.  By  evaporating  to  dryness  a  mixture  of  HgCy2  and  AuCl3. 
Only  part  of  the  Au  is  obtained  as  AuCy,  the  remainder  forming 
a  double  cyanide  of  Au  and  Hg. 

Properties.  —  A  citron-yellow  crystalline  powder,  inodorous, 
tasteless,  unalterable  in  air;  not  affected  by  light  if  dry,  but  in 
presence  of  moisture  takes  a  greenish  tint.  Insoluble  in  water. 

Reactions.  —  1.    Decomposed  by  heat  into  Au  and  CN. 

2.  Burns,  leaving  residue  of  metallic  gold. 

3.  Most  acids  do  not  decompose  it,  even  on  boiling.     When 
recently  precipitated  it  is  soluble  in  some  acids  without  change. 
H2SO4  and  HN03  +  HC1  dissolve  it  slowly  on  boiling.     H2S  does 
riot  decompose  it. 

4.  Ammonia  and  ammonium  sulphide  dissolve  it;  sulphide  of 
gold  is  precipitated  from  the  latter  solution  on  adding  acid. 

5.  KOH,  on  boiling,  gives  Au  and  KAuCy2. 

6.  Dissolves  in  alkaline  cyanides: 

KCy  +  AuCy  =  KAuCy2. 

7.  Dissolves  in  sodium  thiosulphate. 

Auric  Cyanide  (Au(CN)3):  Preparation.  —  1.  By  dissolving 
KAuCy2  in  an  acid  and  evaporating. 

2.  When  potassium  auricyanide  (KAuCy4)  is  treated  with 
excess  of  AgNO3,  a  precipitate  is  formed,  consisting  of  AgAuCy4. 
This,  on  treatment  with  HC1,  decomposes  as  follows: 

AgAuCy4  +  HC1  =  AgCl  +  HCy  +  AuCy3. 

The  filtrate  from  AgCl  is  evaporated  in  vacuo. 

Properties.  —  Small  colorless  crystals,  melting  at  50°  C. 
Easily  soluble  in  water,  alcohol,  or  ether. 

Reactions.  —  1.  Decomposes  on  gentle  heating,  first  giving 
the  aurous  cyanide  AuCy,  then  Au  and  CN. 

2.  Mercurous  nitrate  forms  AuCy  and  HgCy2. 

3.  Oxalic  acid  does  not  precipitate  Au  from  a  solution  of 
AuCy3  in  water. 

Double  Aurous  Cyanides.  —  The  following  are  known : 


SIMPLE  METALLIC  CYANIDES  73 

Auropotassic  cyanide  (KAuCy2). 
Aurosodic  cyanide  (NaAuCy2). 
Auroammonic  cyanide  (NH4AuCy2), 
Aurobarytic  cyanide  (Ba(AuCy2)2). 
Aurozincic  cyanide  (Zn(AuCy2)2). 
Auroargentic  cyanide  (AgAuCy2). 

Aurppotassic  Cyanide  (KAu(CN)2) :  Preparation.  —  - 1.  By  dis- 
solving metallic  gold  in  potassium  cyanide,  in  presence  of  air  or 
oxygen:  4  KCy  +  2Au  +  O  +  H2O  =  2KOH  +  2KAuCy2. 

[This,  and  the  analogous  reaction  with  NaCy,  are  probably  the 
chief  means  by  which  gold  is  dissolved  in  cyanide  treatment]. 

2.  By  dissolving  AuCy  in  KCy  (see  above). 

3.  By  dissolving  oxide  of  gold  or  fulminating  gold  (AuCNO)2 
in  KCy. 

Properties.  —  Crystallizes  in  colorless  plates  composed  of 
orthorhombic  prisms  with  octahedral  faces.  Dissolves  in  4  parts 
of  cold  water  and  0.8  parts  of  boiling  water.  Very  slightly  soluble 
in  alcohol.  Unalterable  in  air. 

Reactions.  —  1.    Decomposed  by  heat  into  Au,  Cy,  and  KCy. 

2.  Slowly  decomposed  by  acids,  giving  off  HCy  and  deposit- 
ing AuCy. 

3.  Not  decomposed  by  H2S. 

4.  Decomposed  by  mercuric  chloride,  forming  a  chlorocyanide 
of  mercury  and  potassium: 

HgCl2  +  KAuCy2  =  KC1  •  HgCy  +  AuCy  +  Cl. 

5.  Forms  addition-products  with  the  haloid  elements,  having 
the  general  formula 

KCyAuCyX2 ,  nH2O  where  X  =  Cl ,  Br  or  I. 

.  Iodine  decomposes  it  into  AuCy,  Cy,  and  KI. 
Aurosodic  Cyanide  (NaAu(CN)2).  —  Its  preparation  and  reac- 
tions are  analogous  to  those  of  KAuCy2.     Also  prepared  by  double 
decomposition,  thus: 

Na2SO4  +  Ba(AuCy2)2  =  BaSO4  +  2NaAuCy2. 

Less  soluble  in  water  than  KAuCy2.     Very  slightly  soluble  in 

alcohol.     Crystallizes  in  anhydrous  scales  which  decompose  at 

about  200°.     Also  forms  addition  compounds  with  Cl,  Br,  and  I. 

Auripotassic  Cyanide  (KAu(CN)4) :  Preparation.  —  1.    By  act- 


74  THE  CYANIDE   HANDBOOK 

ing  on  a  mixture  of  Au  and  AuCl3  with  concentrated  solution  of 
KCy,  and  crystallizing. 

Properties.  —  Colorless  crystals.  Containing  H2O,  which  is 
only  completely  given  off  at  200°  C. 

Reactions.  —  1.  Melts  to  a  brown  liquid,  evolving  Cy  and 
leaving  KAuCy2. 

2.  Slowly  decomposed  by  acids. 

3.  Chlorine  decomposes  it  on  heating,  giving  CNC1.     Iodine 
gives  KAuCy2I2. 

4.  Mercuric  chloride  precipitates  AuCy3. 

HgCl2  +  KAuCy4  =  AuCy3  +  KC1  +  HgClCy2. 

Analogous  compounds:  Auriammonic  cyanide  (NH4Au(CN)4) 
and  auriargentic  cyanide  (AgAu(CN)4). 

Cyanides  of  Silver.  —  Silver  forms  a  cyanide  (AgCN)  and 
double  cyanides  of  the  type  mAg(CN)2. 

Cyanide  of  Silver  (AgCN):    Preparation.  —  1.    By  precipitat- 
ing a  silver  salt  with  HCN  or  a  metallic  cyanide  in  suitable  propor- 
tions.    The  best  method  of  obtaining  it  pure  is  by  precipitating 
the  double  cyanide  of  silver  with  silver  nitrate: 
KAgCy2  +  AgNO3  =  KNO3  +  2AgCy. 

(It  is  thus  obtained  free  from  carbonates,  cyanates,  chlorides  and 
ferrocyanides,  which  might  be  present  in  commercial  KCy  or 
NaCy). 

2.  Many  cyanides,   when   treated,   especially  by  the   aid  of 
heat,  with  AgNO3,  are  decomposed,  yielding  AgCN.     Thus, 

ZnCy2  +  2AgNO3  =  Zn(NO3)2  +  2AgCy. 

3.  By  adding  an  acid  to  a  solution  of  the  double  cyanide: 

KAgCy2  +  HN03  =  KNO3  +  HCy  +  AgCy. 

Properties.  —  White,  curdy  substance  resembling  AgCl.  In- 
soluble in  water  and  in  cold,  moderately  concentrated  acids. 
Turns  brown  on  exposure  to  light.  (According  to  Fresenius,  it 
is  not  affected  by  light.) 

Reactions,  —  1.  When  heated  without  access  of  air,  it  first 
melts,  then  decomposes,  swelling  considerably,  giving  up  CN  and 
leaving  a  compound,  Ag6(CN)3,  which,  on  further  heating,  yields 
N  and  carbide  of  silver  (Liebig). 

2.  Heated  in  contact  with  air  or  oxygen,  it  leaves  only  metallic 
silver. 


SIMPLE   METALLIC  CYANIDES  75 

3.  Chlorine  forms  AgCl  and  CN.     When  the  cyanide  is  com- 
pletely decomposed,  the  CN  unites  with  excess  of  Cl,  forming 
CNC1. 

4.  Sulphur  heated  with  AgCN  gives  AgSCN. 

5.  Hot  acids  decompose  it,  giving  HCN.     It  is  completely 
dissolved  and  decomposed  by  hot  50  per  cent.  H2SO4.     [AgCl  is 
not  decomposed  under  these  conditions]. 

6.  Heated  with  water  in  a  sealed  tube  to  280°  C.,  it  is  decom- 
posed into  Ag  and  (NH4)2CO3. 

7.  Boiling  solution  of  KC1  decomposes  it: 

AgCy  +  KC1  =  AgCl  +  KCy. 

8.  Soluble  in  ammonia,  ammoniacal  salts,  ferrocyanides,  and 
thiosulphates. 

9.  Soluble  in  alkaline  cyanides,  forming  double  salts: 

AgCy  +  KCy  =  KAg(Cy)2. 

10.  Decomposed  by  a  solution  of  sulphur  in  CS2,  forming  com- 
pounds which  appear  to  be  sulphides  of  cyanogen. 

Argento  Potassic  Cyanide  (KAg(CN)2) :  Preparation.  —  1.  By 
dissolving  metallic  silver  in  a  solution  of  potassium  cyanide  in 
presence  of  air  or  oxygen: 

4KCy  +  2Ag  +  O  +  H2O  =  2KOH  +  2KAgCy2. 

2.  By  dissolving  certain  insoluble  salts  of  silver  (e.g.,  AgCN, 
AgCl,  Agl,  Ag4FeCy6,  Ag3FeCyc,  and  AgCNO)  in  an  excess  of 
KCN. 

Properties.  —  Crystallizes  in  colorless,  regular  octahedra,  with 
faces  often  depressed  to  the  center.  Inodorous,  with  metallic 
taste.  Soluble  in  8  parts  of  cold  water,  in  4  parts  water  at  20°  C., 
and  in  1  part  boiling  water.  Also  soluble  in  alcohol. 

Reactions.  —  1.  Decomposed  by  acids  with  formation  of  AgCN 
(see  above). 

2.  Decomposed  by  H2S  or  alkaline  sulphides,  with  precipita- 
tion of  Ag2S: 

2KAgCy2  +  H2S  =  Ag2S  +  2KCy  +  2HCy. 
2KAgCy2  +  K2S  =  Ag2S  +  4KCy. 

3.  Many  metallic  solutions  precipitate  insoluble  double  cyan- 
ides of  silver;  e.g., 

2KAgCy2  +  ZnSO4  =  K,SO4  +  Zn(AgCy2)2. 

4.  Certain  metals,  such  as  zinc,  decompose  the  double  cyanide, 


76  THE  CYANIDE  HANDBOOK 

with  precipitation  of  silver,  probably  as  the  result  of  secondary 
reactions : 

KAgCy2  +  Zn  +  H2O  =  KOH  +  H  +  ZnCy2  +  Ag. 

Other  Double  Cyanides  of  Silver.  —  Among  others,  the  follow- 
ing are  known: 

Argentocyanic  acid  (HAgCy2). 

Sodic  argentocyanide  (NaAgCy2). 

Barium  argentocyanide  (Ba(AgCy2)2  •  H2O). 

Sodio-potassic  argentocyanide  (NaK3(AgCy2)4)  =  NaAgCy2  + 
3KAgCy2. 

Zinc  argentocyanide  (Zn(AgCy2)2). 

Similar  compounds  are  formed  with  Cd,  Ni,  Co,  Mn,  Fe,  Cu, 
Pb,  and  Hg. 

Ammonia  forms  the  compound  NH3AgCy. 

The  compound  AgNO3  •  2AgCy  is  formed  by  dissolving  AgCy  in 
a  concentrated  solution  of  AgNO3. 

Cyanides  of  Other  Precious  Metals.  —  Cyanides  and  various 
classes  of  double  cyanides  are  formed  with  the  platinum  metals 
and  other  less  common  elements,  which  need  not  be  considered 
here. 

CYANIDES  OF  COPPER 

Three  simple  cyanides  have  been  described,  viz.,  cuprous 
cyanide  (Cu2(CN)2),  cupric  cyanide  (Cu(CN)2),  cuproso-cupric 
cyanide  (Cu3(CN)4).  There  are  also  numerous  double  cyanides 
of  various  types. 

Cuprous  Cyanide  (Cu2(CN)2) :  Preparation.  —  1.  By  the  action 
of  HCN  on  recently  precipitated  cuprous  hydrate,  on  cuprous 
chloride  dissolved  in  HC1,  or  on  cupric  chloride  in  presence  of 
S02. 

2.  By  decomposition  of  cupric  cyanide  in  presence  of  water. 

3.  By  precipitation  of  cupropotassic  cyanide  with  acids: 

2KCuCy2  +  H2SO4  =  K2SO4  +  Cu2Cy2  +  2HCy. 

Properties.  —  A  white,  curdy  precipitate,  insoluble  in  water 
and  dilute  acids.  This  is  the  most  stable  of  the  cyanides  of 
copper. 

Reactions.  —  1.  On  heating  it  melts,  giving  off  much  water 
and  leaving  a  swollen  brown  mass. 

2.    Decomposed  by  nitric  acid  with  evolution  of  N2O2. 


SIMPLE  METALLIC  CYANIDES  77 

3.  Dissolves  without  change  in  concentrated  HC1,  and  is  pre- 
cipitated from  this  solution  by  H2O  or  KOH. 

4.  Soluble  in  ammonia  and  in  many  ammonium  salts,  forming 
complex  cyanides. 

5.  Soluble  in  alkaline  cyanides: 

Cu2Cy2  +  2KCy  =  2KCuCy2. 

With  excess  of  KCy,  other  compounds  are  formed  (see  below). 

6.  Decomposed  by  ferric  chloride  in  the  cold,  with  evolution 
of  cyanogen: 

Fe2Cl6  +  Cu2Cy2  =  2FeCl2  +  Cu£\2  +  Cy2. 

7.  Decomposed  by  acetic  acid  in  presence  of  an  oxidizing 
agent,  giving  cyanogen. 

Cupric  Cyanide  (CuCy2):  Preparation.  —  1.  By  treating  car- 
bonate of  copper  with  HCy  in  solution : 

CuCO3  +  2HCy  =  CuCy2  +  H2O  +  CO2. 

2.  By  acting  on  acetate  of  copper  with  HCy. 

3.  By  adding  KCy  to  an  excess  of  a  cupric  salt: 

2KCy  +  CuS04  =  CuCy2  +  K^CX. 

Properties.  —  A  yellowish-brown,  unstable  substance,  only 
known  in  hydrated  condition. 

Reactions.  —  1.  Changes  rapidly  and  spontaneously  at  the 
ordinary  temperature,  forming  greenish  or  yellowish-gray  cuproso- 
cupric  cyanide  (?Cu3Cy4  •  H2O),  which,  on  heating,  gives  Cu2Cy2  + 
Cy. 

Cuproso-Cupric  Cyanides.  —  There  appear  to  be  two  of  these, 

viz- :  Cu2Cy2  •  CuCy2  =  Cu3Cy4. 

2Cu2Cy2  •  CuCy2  =  Cu5Cy6. 

These  are,  perhaps,  only  mixtures  of  Cu2Cy2  and  CuCy2. 
Preparation.  —  1.    By  treating  cuprous  oxide  with  HCy. 

2.  By  adding  HCy  to  CuSO4. 

3.  By  spontaneous  decomposition  of  cupric  cyanide: 

3CuCy2  =  Cu3Cy4  +  Cy2. 

Properties.  —  According  to  mode  of  formation,  it  is  yellowish- 
gray,  or  crystallizes  in  transparent  prisms  of  a  brilliant  canary- 
green  color. 

Reactions.  —  1.  Heated  to  100°  it  loses  Cy  and  water,  and  is 
converted  into  Cu2Cy2  without  change  of  form. 


78  THE  CYANIDE   HANDBOOK 

2.  Strong  acids  liberate  HCy,  leaving  a  mixture  of  cuprous 
and  cupric  salts. 

3.  Alkalis  form  double  salts  of  copper  and  the  alkali  metal, 
probably  3Cu2Cy2  •  4mCy,  and  precipitating  Cu(OH)2. 

4.  Alkaline   cyanides  give   (when  in  excess)    the   compound 
Cu2Cy2  •  6mCy.     (m  =  K,  Na,  etc.) 

5.  Ammonia  dissolves  it  to  a  blue  solution.     The  compound 
is   only  slightly  soluble,  and   sometimes   deposits   green   crystals 
(see  below). 

6.  Ammonium  carbonate  dissolves  it  in  the  cold,  other  ammo- 
nium salts  only  on  heating. 

Double  Cyanides  of  Copper.  —  These  are  very  numerous,  the 
best  known  being  those  of  ammonium  and  potassium.  The  ammo- 
nio-cyanides  of  copper  are  of  two  distinct  kinds,  represented  re- 
spectively by  the  formulae.1 

(a)  x(NH4Cy)y(CuCy2)z(Cu2Cy2); 
(6)  x(NH3)y(CuCy2)z(Cu2Cy2). 

The  potassium  compounds  have  the  general  formula,  x(KCy) 
y(Cu2Cy2). 

Double  Cyanides  of  Copper  and  Ammonium.  — The  compounds 
of  class  (a),  which  are  true  double  cyanides  of  copper  and  ammo- 
nium, are  colorless,  highly  soluble,  and  stable  in  absence  of  other 
metallic  salts.  They  act  feebly  as  solvents  of  gold.  They  are 
decomposed  by  excess  of  a  copper  salt,  yielding  a  mixture  of 
cuprous  and  cupric  cyanides. 

The  compounds  of  the  second  class  (6),  having  the  formula 
x(NH3)y(CuCy2)z(Cu2Cy2),  are  formed  by  dissolving  mCuCy2  -f 
nCu2Cy2  in  ammonia.  They  are  generally  regarded  as  cupram- 
monium  cyanides,  i.e.,  as  compounds  in  which  the  ammonia  is 
intimately  united  with  copper,  forming  a  complex  radical,  to 
which  Rose2  gives  the  formula  Cu(NH3)4  (cuprammonium),  and 
which  enters  into  unstable  combinations  with  cyanogen. 

These  substances  are  generally  blue  or  green  crystalline  bodies, 
only  slightly  soluble  in  water.  They  yield  deep  blue  solutions 

and  appear  to  be  "ionized"  in  dilute  solutions,  with  liberation  of 

+      + 

CN  and  the  cuprammonium  ion  Cu(NH3)4,  to  which  the  blue 
color  of  the  liquid  is  due. 

i  Sulman,  Trans.  I.  M.  M.,  XIV,  363. 
a  Trans.  I.  M.  M.,  XIV,  369. 


SIMPLE  METALLIC  CYANIDES  79 

Preparation  and  Properties.  —  1.  When  a  salt  of  copper  is 
precipitated  by  ammonium  cyanide,  cyanogen  is  abundantly 
evolved  and  a  greenish-blue  substance  formed  having  the  formula 
2NH3  •  CuCy2  •  Cu2Cy2  •  H2O.  This  is  an  amorphous  powder, 
slightly  soluble  in  cold  water  and  decomposed  at  100°  C. 

2.  By  acting  on  the  above  with  further  quantities  of  ammonia, 
a  blue  liquid  is  obtained  which,  on  evaporation,  yields  4NH3. 
CuCy2 .  2Cu2Cy2,  in  small,  bright-green,  needle-like  crystals,  pris- 
matic, with  metallic  luster. 

The  same  substance  is  obtained  by  passing  a  current  of  HCN 
into  oxide  of  copper  suspended  in  ammonia. 

3.  When  the  preceding  compound  is  heated  with  ammonia 
and  a  current  of  NH3  gas  is  passed  through  the  liquid,  the  latter 
deposits,  on  cooling,  the  substance  6NH3  •  CuCy2  •  Cu2Cy2.     This 
is   a  crystalline  precipitate,  in  prismatic  needles  of  a  fine  blue 
color.      Exposed  to  the  air,  it  loses  NH3  and  becomes  green. 

Reactions.  —  Solutions  of  these  compounds  readily  give  up 
cyanogen  to  any  substance  capable  of  combining  with  it.  Hence 
they  act  as  powerful  solvents  of  gold.  This  reaction  is  accom- 
panied by  deposition  of  the  slightly  soluble  dicuproso-cupric 
cyanide  4NH3  •  CuCy2  •  Cu2Cy2,  and  takes  place  without  the 
intervention  of  oxygen. 

Double  Cyanides  of  Copper  and  Potassium.  —  The  following 
are  known: l 

(a)    4KCy  •  3Cu2Cy2. 
(6)    2KCy-Cu2Cy2. 

(c)  4KCyCu2Cy2. 

(d)  6KCyCu2Cy2. 

Preparation  and  Properties.  —  (a)  The  first  of  these  is  ob- 
tained by  the  action  of  fused  cuprous  cyanide  on  potash  and  is 
little  known. 

(6)  This  compound  is  formed  by  the  action  of  KCy  on  Cu2Cy2 
in  the  proportions  indicated  by  the  formula  of  the  compound.  It 
is  also  formed  by  acting  on  cupric  hydrate  with  KCN  solution  and 
slowly  evaporating,2  or  by  acting  on  cuproso-cupric  cyanide  with 
KCN. 

It  forms  transparent,  colorless  clinorhombic  prisms,  fusible 

»  Sulman,  Trans.  I.  M.  M.,  X,  125. 
»  Virgoe,  Ibid.,  X,  107. 


80  THE  CYANIDE   HANDBOOK 

without  decomposition,  but  liberating  metallic  copper  on  con- 
tinued fusion. 

The  compound  2KCy  •  Cu2Cy2  is  sparingly  soluble  in  water, 
and  partially  decomposes  in  solution  into  Cu2Cy2  and  6KCy 
Cu2Cy2.  It  is  not  a  solvent  of  gold  or  silver. 

(c)  This   compound,    4KCy  •  Cu2Cy2,   is   the   form   in   which 
copper,  according  to  Virgoe  (loc.  cit.,  p.  141),  normally  exists  in 
cyanide   solutions,  though    Sulman   (loc.   cit.,   p.    127)    considers 
that  it  is  more  frequently  present  as  sulphocyanide  (Cu2(SCy)2) 
dissolved  in  KCy. 

It  is  prepared  by  agitating  cupric  hydrate  with  excess  of  KCy: 
i  2Cu(OH)2  +  8KCy  =  4KCy  •  Cu2Cy2  +  4KOH  +  Cy2. 

Virgoe  considers  that  an  intermediate  product  exists,  to  which 
he  gives  the  formula  2KCy  •  Cu2Cy2  •  4KCy  •  Cu2Cy2,  which  might 
be  written  3KCy  •  Cu2Cy2.  This  latter  is  said  to  be  a  good  solvent 
of  gold  and  silver  (loc.  cit.,  p.  142). 

(d)  6KCy  •  Cu2Cy2.     This  is  obtained  by  dissolving  metallic 
copper  in  KCN: 

Cu2  +  8KCy  +  H2O  +  O  =  6KCy  •  Cu2Cy2  +  2KOH. 

Colorless  transparent  prisms,  with  6  sides,  terminated  by  6-sided 
pyramids,  almost  unalterable  in  air,  but  gradually  becoming  blue. 
May  be  fused  with  separation  of  a  little  copper.  [The  salts  de- 
scribed by  Virgoe  as  existing  in  solution  may  possibly  be  only  mix- 
tures of  2KCy  •  Cu2Cy2  and  6KCy  •  Cu2CyJ. 

Reactions.  — •  1.  The  double  cyanides  of  K  and  Cu  are  all 
decomposed  by  acids,  forming  Cu2Cy2  and  HCy. 

2.  H2S  does  not  precipitate  copper  sulphide  from  their  solu- 
tions, or  only  to  a  very  slight  extent  from  dilute  solutions.     Alka- 
line sulphides  give  no  precipitate. 

3.  Ferric  salts  precipitate  Cu2Cy2,  Fe(OH)6  and  liberate  HCy. 

4.  Mercuric  salts  give  Cu2Cy2,  HgCy2,  and  the  potassium  salt 
of  the  radical  originally  combined  with  the  mercury. 

5.  Excess  of  copper  salts  give  a  pale  yellow  precipitate  which 
may  be  a  cuproso-cupric  cyanide  —  xCuCy2  •  yCu2Cy2. 

6.  Silver  nitrate  converts  a  part  of  the  KCy  in  these  compounds 

1  The  reaction  (in  presence  of  an  excess  of  alkali)  which,  according  to  the 
writer's  experiments,  seems  most  in  accordance  with  the  facts,  is  as  follows: 

2Cu(OH)2  +  7KCy  =  4KCy  •  Cu2Cy2  +  2KOH  +  KCyO  +  H2O 
This  indicates  a  consumption  of  3.6  parts  KCy  for  every  part  of  Cu  dissolved. 


SIMPLE   METALLIC  CYANIDES  81 

into  the  soluble  KAgCy2  before  any  precipitation  of  AgCy  takes 
place.     The  usual  reaction  is  (Virgoe,  loc.  cit.,  p  139): 

AgN03  +  4KCy  Cu2Cy2  =  2KCy  -Cu2Cy2  +  KAgCy.  +  KNO3. 

On  further  addition  of  AgNO3,  there  is  a  precipitation  of  Cu2Cy2 
as  follows: 

AgNO3  +  2KCy  -Cu2Cy2  =  Cu2Cy2  +  KAgCy2  +  KNO3. 

When  KI  is  added,  however,  there  is  an  immediate  precipitation 
of  Agl,  which  is  not  soluble  in  the  cupropotassic  cyanides. 

Other  Double  Cyanides  of  Copper. —  Other  compounds  are  de- 
scribed with  Na,  Ba,  Zn,  Mn,  Co,  Ni,  Fe,  Pb,  and  other  metals. 

CYANIDES  OF  MERCURY 

Only  one  well-defined  simple  cyanide  exists,  namely,  mercuric 
cyanide  (Hg(CN)2). 

There  are  two  basic  cyanides  (oxycy anides) ,  namely,  HgO- 
HgCy2,  and  HgO  •  3HgCy2,  besides  numerous  double  cyanides  with 
the  alkali  metals  and  ammonia. 

Many  chlorocyanides  are  also  known,  of  the  general  formula 
HgCy2  •  RC1  +  nH2O. 

Mercuric  Cyanide  (Hg(CN)2) :  Preparation.  —  1.  By  action  of 
HCy  on  mercuric  oxide  suspended  in  water: 

2HCy  +  HgO  =  HgCy2  +  H2O. 

2.  By  double  decomposition  of  mercuric  salt  and  hydrocyanic 
acid:  Hg(NO3)2  +  2HCy  =  HgCy2  +  2HNO3. 

[With  mercurous  salts  a  mixture  of  HgCy2  and  metallic  mer- 
cury is  obtained]. 

3.  By  the  action  of  mercuric  oxide  on  cyanides  or  ferrocyan- 
ides,  or  (with  boiling)  on  Prussian  blue. 

4.  By  heating  mercuric  sulphate  with  ferrocyanide. 

5.  By  acting  on  the  ferrocyanides  of  lead  or  barium  with 
mercuric   sulphate,   and   filtering  from  the  insoluble   PbSO4  or 
BaSO4. 

Properties.  —  Crystallizes  in  colorless,  rectangular  prisms  with 
square  base,  but  occurs  in  other  forms.  Anhydrous.  Soluble  in 
8  parts  cold  water;  more  soluble  in  hot  water.  Insoluble  in  abso- 
lute alcohol. 

Reactions.  —  1.    On  heating,  gives  Hg  and  (CN)2  (see  above). 


82  THE  CYANIDE  HANDBOOK 

2.  Decomposed  by  concentrated  acids,  giving  HCN  and  the 
corresponding  mercury  salt. 

3.  Chlorine  in  the  presence  of  moisture  or  on  exposure  to 
light  gives  HgCl2  and  CNC1. 

Bromine  and  iodine  act  similarly. 

4.  Water  at  280°  C.  forms  Hg  and  (NH4)2CO3. 

5.  Decomposed  by  HC1,  HBr,  HI,  and  H2S,  giving  the  corre- 
sponding Hg  salt  and  HCy.     Gradually  decomposed  by  alkaline 
sulphides,  forming  HgS  and  a  thiocyanate  of  the  alkali. 

Basic  Cyanides  of  Mercury.  —  These  are  white  or  yellowish 
crystalline  explosive  bodies,  formed  by  acting  on  HgCy2  with 
HgO  in  various  proportions. 

Double  Cyanide  of  Mercury  and  Potassium  (K2Hg(Cy)4): 
Preparation.  —  1.  By  dissolving  HgCy2  in  KCy  and  evaporating 
till  the  salt  crystallizes: 

HgCy2  +  2KCy  =  K2HgCy4. 

2.  By  treating  HgCy2  with  HCy  and  K2CO3: 

HgCy2  +  2HCy  +  K2CO3  -  K2HgCy4  +  H2O  +  CO2. 

3.  By  dissolving  HgO  in  KCy: 

HgO  +  4KCy  +  H2O  =  K2HgCy4  +  2KOH. 

4.  By  dissolving  HgCl2  in  KCy: 

HgCl2  +  4KCy  =  K2HgCy4  +  2KC1. 

Properties.  —  Crystallizes  in  regular  octahedra.  Transparent. 
Unalterable  in  air.  Dissolves  in  4  parts  cold  water.  Solution 
smells  slightly  of  HCy. 

Reactions.  —  1  .  Decrepitates  violently  on  heating,  and  melts 
to  a  brown  liquid  which  gives  off  Cy2  and  Hg. 

2.  Decomposed  by  acids,  either  completely  or  with  formation 
of  HgCy2  and  HCy. 

4HC1  +  K2HgCy4  =  2KC1  +  HgCl2  +  4HCy. 
2HN03  +  K2HgCy4  -  2KNO3  +  HgCy2  +  2HCy. 

3.  Decomposed  by  alkaline  sulphides  or  by  H2S  with  precipi- 
tation of  HgS  :        KjS  +  K2HgCy4  =  Hgg  +  4RCy 


4.    Acts  as  a  solvent  of  gold  and  silver,  with  deposition  of 
mercury  and  without  intervention  of  oxygen: 

K2HgCy4  +  2Au  =  Hg  +  2KAuCy2. 
K2HgCy4  +  2Ag  =  Hg  +  2KAgCy2. 


SIMPLE  METALLIC  CYANIDES  83 

5.  Decomposed  by  other  metals  (zinc,  for  example)  with 
deposition  of  mercury: 

K2HgCy4  +  Zn  =  K2ZnCy4  +  Hg. 

[A  similar  double  cyanide  is  formed  with  sodium,  namely, 
Na2HgCy4.  Double  cyanides  of  mercury  with  Zn  and  Pb  are 
also  known. 

Many  double  salts  are  formed  by  combination  of  HgCy2  with 
other  metallic  salts,  e.g.,  nitrates,  thiosulphates,  thiocyanates, 
ferrocyanides,  etc. 

CYANIDES  OF  LEAD 

No  simple  cyanide  of  lead  of  the  formula  Pb(CN)2  is  known. 
The  precipitate  obtained  by  acting  on  lead  salts  with  an  alkaline 
cyanide  appears  to  have  the  composition  2PbO  •  Pb(CN)  2  •  H2O.  It 
is  best  prepared  by  acting  on  neutral  lead  acetate  with  KCN  in 
presence  of  ammonia. 

It  is  a  white  precipitate,  insoluble  in  water,  but  decomposed 
by  dilute  acids  with  evolution  of  HCy. 

Double  Cyanide  of  Zinc  and  Lead.  —  When  a  salt  of  lead  is 
precipitated  by  K2ZnCy4,  a  white  precipitate  is  obtained  having 
the  composition  2ZnCy2  •  PbCy2. 


SECTION  III 

METALLIC    COMPOUNDS   OF    COMPLEX 
CYANOGEN   RADICALS 

(A)    METALLIC  COMPOUNDS  OF  THE  RADICAL  RC6N6 

THE  compounds  we  now  have  to  consider  cannot  legitimately 
be  described  as  cyanides.  Although  under  certain  conditions 
they  may  be  obtained  from,  or  may  yield,  cyanogen  or  cyanides 
of  the  type  previously  discussed,  they  differ  widely  from  the 
cyanides  in  their  general  properties  and  reactions,  and  behave 
as  though  containing  a  negative  radical  into  the  composition  of 
which  a  metal  (usually  of  the  iron  type)  enters  as  a  constituent 
part.  This  radical  goes  in  and  out  of  combination  unchanged, 
and  may  be  replaced  by  different  non-metallic  elements  or  rad- 
icals. 

The  general  formula  for  this  radical  is 

RC6N6, 

where  R  is  an  atom  of  a  metal  such  as  Fe,  Mn,  Cr,  Co,  or  of  the 
platinum  group,  such  as  Pt,  Ir,  Pd,  Os,  Rh,  Ru. 

A  closely  related  class  of  substances,  known  as  the  nitroprus- 
sides,  contain  the  radical 

RC5N6O,  probably  RC5N5(NO). 

The  radical  RC6N6  is  capable  of  acting  as  a  dyad,  triad,  or 
tetrad,  forming  compounds  of  the  types  — • 

M2  •  RC6N6  where  M  represents  an 

M3  •  RC6N6  atom  of  a  monad  element  or 

M4  •  RC6N6  group. 

Compounds  of  the  first  type  are  very  unstable;  those  of  the 
second  may  perhaps  have  the  constitution 

M3EE(RC6N6) 

I 

M3=(RC0N6)  on  the  assumption  that  the  group  RC0N6 
is  normally  tetrad. 

84 


COMPLEX   METALLIC    CYANIDES  85 

COMPOUNDS    IN    WHICH    IRON    ENTERS    INTO    THE    NEGATIVE 

RADICAL 
These  compounds  are  as  follows: 

(a)  Ferrocyanides,  M4FeC6N6. 

(b)  Ferricyanides,  M3FeC6N6. 

(c)  Perferricyanides,  M2FeC6N6.     (?) 

(d)  Nitroprussides,  M2Fe(CN)5  •  (NO). 

For  simplicity  we  may  use  the  symbol  FeCy6  to  indicate  the 
radical  FeC6N6  in  the  first  three  of  these  groups  of  compounds. 

(a)    FERROCYANIDES  (M4FeCy6). 

General  Characteristics. —  1 .   Most  f errocyanides  are  colored ;  the 
characteristic  colors  of  these  compounds  are  of  value  in  analysis. . 

2.  The  soluble  alkali  ferrocyanides  are  non-poisonous. 

3.  They  do  not  evolve  HCN  when  treated  with  very  dilute 
acids,  but  generally  yield  hydroferrocyanic  acid  (E^FeCyg) . 

4.  Those  ferrocyanides  which  are  completely  dehydrated  by 
heat  without  decomposition  yield  on  further  heating  N  and  car- 
bide of  iron.     In  addition  to  these  there  may  be  formed  a  cyanide 
or  carbide  of  the  positive  metal,  or  the  metal  may  be  liberated 
with  evolution  of  (CN)2. 

5.  Those  ferrocyanides  which  cannot  be  completely  dehydrated 
without  decomposition  yield  HCN,  NH3,  CO2  and  a  mixture  or 
compound  of  each  of  the  metals  with  carbon. 

6.  When  aqueous  solutions  of  alkali  ferrocyanides  are  electro- 
lyzed,  the  alkali  separates  at  the  —  pole,  and  HCN  and  Prussian 
blue  at  the  +  pole;  in  some  cases  a  cyanide  of  the  metal  forming 
the  electrode  is  produced. 

7.  When  heated  with  concentrated  H2SO4,  sulphates  of  Fe, 
NH4,  and  the  metal  forming  the   +   radical  are  produced,  and 
SO2,  CO,  CO2,  and  N  are  evolved. 

8.  H2S    has    no    action    on    alkaline    ferrocyanides.      Some 
others  are  decomposed,  giving  a  sulphide  of  the  +  radical,  and 
H4FeCy6. 

9.  Ferrocyanides  of  heavy  metals  are  generally  decomposed 
by  aqueous  alkalis,  giving  a  ferrocyanide  of  the  alkali  and  hydrate 
of  the  heavy  metal. 

10.  Decomposed  by  boiling  with  HgO  and  water,  forming 
HgCy2  and  oxides  or  hydrates  of  the  metals. 


86  THE  CYANIDE   HANDBOOK 

11.  Alkaline  ferrocyanides  are  converted  into  the  correspond- 
ing ferricyanides  by  oxidizing  agents. 

Potassium  Ferrocyanide  (K4FeCy6  •  3H20) :  Preparation.  — 
1.  By  boiling  Prussian  blue  with  potash: 

Fe4(FeCy6)3  +  12KOH  =  3K4FeCy6  +  4Fe(OH)3. 

2.  By  fusing  nitrogenous  animal  matter  with  K2CO3  and  scrap 
iron,  lixiviating  with  water,  filtering,  and  crystallizing.     KCy  is 
first  formed,  which  reacts  on  the  iron  compounds  during  the  extrac- 
tion with  water,  yielding  K4FeCy6.     [This  process  will  be  dis- 
cussed more  fully  under  the  heading  "Manufacture  of  Cyanide."] 

3.  By  heating  ammonium  thiocyanate  (NH4SCN)  with  scrap 
iron  to  dull  redness  and  extracting  with  water. 

4.  By  action  of  KCN  on  ferrous  compounds: 

2KCN  +  FeSO4  =  K2SO4  +  Fe(CN)2. 
4KCN  +  Fe(CN)2  =  K4Fe(CN)6. 

Similarly  with  FeS,  FeCO3,  Fe(OH)2,  etc. 

5.  By  acting  upon  various  metallic  ferrocyanides  with  KOH. 
Properties.  —  Crystallizes   with   3    molecules   H2O    as   yellow 

quadratic  pyramids.  Non-poisonous.  Loses  water  at  60°  to  80° 
C.  Unchanged  at  ordinary  temperatures.  Soluble  in  4  parts 
cold  and  2  parts  boiling  water.  Insoluble  in  alcohol. 

Reactions.  —  1.  Heated  in  a  closed  vessel,  it  melts  a  little 
above  red  heat,  evolves  N,  and  leaves  a  mixture  of  Fe  carbide 
and  KCy.  When  the  hydrated  salt  is  used,  C02,  NH3,  HCN,  and 
N  are  evolved. 

2.  Aqueous  solution  is  gradually  decomposed  on  exposure  to 
light,  forming  Prussian  blue  and  evolving  HCN. 

3.  When  heated  to  redness  in  air,  or  with  reducible  metallic 
oxides,  it  gives  KCyO.     Ozone  changes  it  slowly  into  K3FeCy6. 
Oxidizers  such  as  KMnO4,  MnO2,  PbO2,  etc.,  also  form  K3FeCy6: 

2K4FeCy6  +  RO2  =  RO  +  K2O  +  2K3FeCy6. 

Chlorine  and  bromine  act  as  follows: 

2K4FeCy6  +  C12  =  2KC1  +  2K3FeCy6. 
Iodine  gives  a  double  compound  of  KI  and  K3FeCy6. 

4.  1  On  electrolysis  it  gives  K3FeCy6  at  the  +  pole  and  KOH 
and  H  at  the  —  pole  (Joannis). 

1  According  to  Morley  and  Muir  (Watts,  "  Diet,  of  Chemistry,"  II,  333), 
when  aqueous  solutions  of  alkali  ferrocyanides  are  electrolyzed,  alkali  separates 
at  the  -  pole  and  HCy  and  Prussian  blue  at  the  +  pole. 


COMPLEX   METALLIC    CYANIDES  87 

5.  Dilute  cold  sulphuric  acid  gives  H4FeCy6: 

K4FeCy6  +  2H2SO4  =  H4FeCy6  +  2K£O<. 
Dilute  warm  sulphuric  acid  gives 

2K4FeCy6  +  3H2SO4  =  3K2SO4  +  K2Fe  •  FeCy6  +  6HCy. 
Concentrated  sulphuric  acid  gives 
K4FeCy6  +  6H2SO4  +  6H2O  =  2K2SO4  +  3(NH4)2SO4  +  FeSO4  4-  6CO. 

6.  Fairly  concentrated    HNO3    (say  50   per   cent.    HNO3   by 
volume)  forms  nitroprussic  acid  (H2FeCy5  •  NO  •  H2O). 

Very  concentrated  HNO3  decomposes  K4FeCy6  into  N,  CN, 
NO,  CO2,  KNO3  and  Fe2O3. 

7.  Boiled  with  mercuric  oxide: 

K4FeCy6  +  3HgO  +  3H2O  =  3HgCy2  +  4KOH  +  Fe(OH)2. 

8.  Boiled  with  NH4C1,  it  gives  NH4Cy,  which  volatilizes: 

K4FeCy«  +  6NH4C1  =  6NH4Cy  +  4KC1  +  FeCl2. 

9.  Heated  with  ammoniacal  silver  nitrate,  it  forms  Fe(OH)3 
and  KAgCy2. 

10.  Most  metallic  salts  give  precipitates  of  insoluble  ferro- 
cyanides. 

CHARACTERISTIC  INSOLUBLE  FERROCYANIDES 
The  more  important  of  these  are  as  follows: 

Barium  BaFeCy6  -  6H2O  White,  slightly  sol- 

uble. 

Cobalt  Co2FeCy6  •  7H2O  Blue,  changing  to 

red. 

Copper  Cu2FeCy6  •  xH2O  (cupric)  Reddish  brown. 

Iron  Fe2(FeCy6)  (ferrous)  White. 

Fe4(FeCy6)3  (ferric)  Blue. 

Lead  Pb2FeCy6  -  3H2O  White. 

Manganese     Mn2FeCy6  •  7H2O  White. 

Mercury         composition  doubtful  White. 

Nickel  Ni2FeCy6  -  (7  to  1 1)  H2O  Greenish  white. 

Tin  Sn2FeCy6  •  4H2O  (stannous)  White. 

"  SnFeCy6  •  4H2O  (stannic)  Brownish. 

Zinc  Zn2FeCye  •  3H2O  White. 

Silver  Ag2FeCy6  White. 


88  THE  CYANIDE  HANDBOOK 

The  more  important  soluble  ferrocyanides  are  those  of  NH4,  Ca, 
H,  Mg,  Na,  K. 

There  are  also  numerous  compounds  in  which  more  than  one 
metal  forms  part  of  the  positive  radical,  for  example,  K2ZnFeCy8. 
Hydrogen  Ferrocyanide : 

Hydroferrocyanic  Acid  (H4FeCy6).  —  This  is  the  acid  corre- 
sponding to  the  metallic  ferrocyanides.  It  may  be  prepared: 

1.  By  decomposing  Ba2FeCy6  with  an  equivalent  of  H2S04, 
and  filtering  from  BaSO4. 

2.  By  the  action  of  cold  concentrated  HC1  on  an  air-free  solu- 
tion of  K4FeCy6,  and  washing  the  precipitate  with  alcohol  and 
ether. 

Properties.  —  A  white,  crystalline  powder,  becoming  blue  in 
moist  air  with  evolution  of  HCy.  Soluble  in  water.  Strongly 
acid  to  litmus. 

Reactions.  —  Solution  decomposes  carbonates,  acetates,  oxal- 
ates,  and  tartrates.  When  boiled  with  water  it  decomposes: 

2H4FeCy6  =  FeH2(FeCy6)  +  6HCy. 
Ferrocyanides  of  Copper: 

Cuprous  Ferrocyanide  (Cu4FeCy6)  is  said  to  be  formed  by  add- 
ing K4FeCy6  to  Cu2Cl2  dissolved  in  HC1. 

Cupric  Ferrocyanide  (Cu2(FeCy6)  •  xH20)  is  formed: 

1.  By  adding  K4FeCy6  to  a  cupric  salt.     By  this  means  the 
precipitate  formed  is  mixed  with  double  ferrocyanidesCuK2(FeCy6), 
and  Cu3K2(FeCy6)2. 

2.  By  adding  H4FeCy6  to  a  cupric  salt.     A  reddish-brown   pre- 
cipitate, insoluble  in  dilute  acids;  soluble  in  ammonia  and  alkalis. 

Ferrocyanides  of  Iron: 

Ferrous  Ferrocyanide  Fe2(FeCy6).  —  Obtained  by  adding  fer- 
rous salts  to  H4FeCy6,  both  compounds  being  freed  from  air  and 
ferric  compounds.  A  white  amorphous  precipitate,  soon  oxidiz- 
ing, with  formation  of  blue  compounds: 

3Fe2  (FeCy6)  +  3O  +  3H2O  =  Fe2(OH)6  +  Fe4(FeCy6)3. 

Potassium  Ferrous  Ferrocyanide  (K2  •  Fe  •  FeCy6)  (Everitt's 
salt).  —  Obtained  by  decomposing  K4FeCy6  with  hot  dilute  sul- 
phuric acid.  (See  under  "  Potassium  Ferrocyanide.  ") 

White,  microscopic  quadratic  crystals,  becoming  blue  in  air. 
Converted  by  oxidizers  into  potassium-ferrous  ferricyanide 
(FeK-FeCy6). 


COMPLEX   METALLIC   CYANIDES  89 

Ferric  Ferrocyanide  (Prussian  Blue:  Fe4(FeCy6)3) :  Prepara- 
tion. —  1.  By  acting  on  a  ferric  salt  with  potassium  ferrocyanide, 
keeping  the  ferric  salt  in  excess: 

3K4FeCy6  +  4FeCl3  =  12KC1  +  Fe4(FeCy6)3. 

2.  By  acting  on  a  soluble  cyanide  with  a  ferrous  and  ferric 
salt,  adding  excess  of  KOH  or  NaOH,  then  excess  of  acid: 

(a)  6KCy  +  FeSO4  =  K2SO4  +  K4FeCy6. 
(6)  3K4FeCy6  +  4FeCl3  =  12KCI  +  Fe4(FeCy6)3. 

3.  Prussian  blue  is  obtained  commercially  by  mixing  K4FeCy6 
with  partially  oxidized  ferrous  sulphate,  and  heating  the  light- 
blue  precipitate  so  obtained  with  various  oxidizing  agents.     In 
addition  to  ferric  ferrocyanide  (Fe4(FeCy6)3)  it  usually  contains 
also  —  Ferrous  ferrocyanide   (Fe2  •  FeCy 6) ,    Ferrous  ferricyanide 
(Fe3(FeCy6)2,)  and  sometimes  Everitt's  salt  (K2Fe  •  FeCy 6) . 

Properties.  —  A  dark-blue  amorphous  solid  with  luster  re- 
sembling that  of  copper.  Retains  water  up  to  250°  C.,  at  which 
temperature  it  begins  to  decompose.  Insoluble  in  water,  alco- 
hol, ether,  and  dilute  acids. 

Reactions.  —  1.  When  strongly  heated  it  ignites,  leaving 
Fe203.  Heated  in  a  partially  closed  vessel,  it  first  gives  off  NH4Cy 
and  (NH4)2CO3,  and  finally  HCN,  CO,  and  CO2. 

2.  Alkalis    (including    MgO)    decompose    it,    yielding    ferric 
hydrate  and  a  ferrocyanide  of  the  alkali. 

Ammonia  gives  Fe(OH)3  and  (NH4)4FeCy6. 
Alkaline  carbonates  give  similar  reactions. 

3.  Boiled  with  HgO  and  water,  it  gives  Fe2O3  and  HgCy2. 

4.  Boiled  with  lead  oxide,  it  gives  lead  ferrocyanide,  a  ferri- 
cyanide, and  Fe203. 

5.  Reduced  by  H2S  or  by  Fe  or  Zn,  it  gives  white  ferrous  ferro- 
cyanide (Fe2-FeCye). 

Sodium  Ferrocyanide  (Na4FeCy0-  12H20). — Obtained  by  boil- 
ing Prussian  blue  with  NaOH,  filtering,  and  cooling.  Pale  yellow 
monoclinic  crystals,  which  effloresce  in  air.  Reactions  similar  to 
those  of  K4FeCy6. 

Zinc  Ferrocyanide  (Zn2FeCy6-3H2O). — Obtained  pure  by  add- 
ing excess  of  ZnSO4  to  H4FeCy6.  The  precipitates  formed  by 
ZnS04,  or  other  zinc  -salts,  with  ferrocyanides  contain  more  or  less 
of  double  ferrocyanides  of  zinc  and  the  alkali  metal. 

White  precipitate,  insoluble  in  dilute  acids,  soluble  in  alkalis 


90 


THE  CYANIDE  HANDBOOK 


and  ammonia.  Double  salts  are  also  formed  with  ammonia,  one 
of  which  is  Zn2FeCy6  •  3NH3  -  H2O. 

The  white  precipitate  found  in  the  zinc-boxes  used  in  precipi- 
tation of  gold-cyanide  solutions,  and  formed  when  insufficient 
alkali  is  present,  appears  to  be  a  mixture  of  ZnCy2,  Zn(OH)2  and 
double  ferrocyanides,  to  which  the  formulae  K2Zn(FeCy6)  and 
K2Zn3(FeCye)2  have  been  assigned.1  (See  Section  V:  "  Chemistry 
of  Precipitation. ") 

(b)    FERRICYANIDES  (M3FeCy6) 

These  substances  are  formed  generally  by  the  action  of  oxidiz- 
ing agent  on  ferrocyanides: 

2M4FeCy6  +  RO  =  M2O  +  R  +  2M3FeCy6; 

where  RO  represents  any  substance  containing  "  available"  oxygen. 
The  alkali  ferricyanides  are  soluble  in  water:  most  others  are 
insoluble.  Many  have  characteristic  colors.  They  act  as  oxidiz- 
ing agents  by  reaction  the  converse  of  that  given  above. 

CHARACTERISTIC  FERRICYANIDES 


Metal 

Color 

Solubility,  etc. 

NH4  

Ruby-red 

Soluble 

Ca 

Red 

Co 

Red-brown 

fCu'  . 

Brown-red 

Insoluble  (cuprous} 

CuW  

Fe" 

Yellowish 
Blue 

Insoluble  (cupric) 

Fe'Fe"'  

Green 

Insoluble  (forrosoferric) 

H 

Pb  

Dark  red 

Mg  . 

Red-brown 

Snlnhlp 

Mn     . 

Brown 

Ni 

K 

Red 

q0lnuia 

Ae.. 

Orange-yellow 

Na  

Ruby-red 

Sn 

White 

The  insoluble  ferricyanides  are  soluble  in  alkalis  and  ammonia. 
Potassium  Ferricyanide  (K3FeCy6) :  Preparation.  —  1.    By  act- 

1  "Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa/'  V.  56,  75. 


COMPLEX   METALLIC    CYANIDES  91 

ing  upon  K4FeCy6  with  Cl,  Br,  ozonized  oxygen,  PbO2,  KMnO4,  or 
bleaching  powder.     In  some  cases  the  action  requires  the  presence 
of  an  acid,  thus: 
5K4FeCy6  +  4H2SO4  +  KMnO4  =  SKsFeCve  +  3K2SO4  +  MnSO4  +  4H2O. 

When  chlorine  is  used,  it  is  passed  into  cold  solution  of  K4FeCy6, 
with  constant  agitation,  till  a  few  drops  of  the  liquid  give  a  brown- 
red  color  with  FeCl3,  instead  of  a  blue  color. 

K3FeCy6  is  also  one  of  the  products  of  electrolysis  of  K4FeCy6. 

Properties.  —  Large  red  prismatic  monoclinic  crystals.  More 
soluble  in  hot  than  in  cold  water.  Nearly  insoluble  in  alcohol. 

Reactions.  —  1.  Heated  in  a  closed  vessel,  it  decrepitates, 
evolves  (CN)2  and  a  little  N,  leaving  a  residue  of  KCy,  K4FeCy6, 
Fe4(FeCy6)3,  C,  Fe,  and  probably  paracyanogen  (CN)x. 

2.  Heated  in  air  (CN)2  is  evolved,  and  Fe2O3  and  KCy  remain. 

3.  Reduced  to  K4FeCy6  by  many  reagents,  such  as  H2S,  Na2S, 
Na2S2O3;  also  by  finely  divided  metals  (Ag,  Fe,  Zn,  etc.),  by  SO2, 
by  hot  ferrous   salts,  phosphites,  etc.,  especially  in  presence  of 
alkalis.     The  general  type  of  these  reactions  may  be  represented 
thus:  KsFeCye  +  KOH  +  R  -  KJFeCye  +  R  -  OH. 

R  being  an  oxidizable  substance. 

4.  Certain  metallic  oxides  (e.g.,  PbO,  Cr2O3,  MnO,  SnO,  etc.), 
when  boiled  with  K3FeCy6  in  presence  of  KOH,  pass  to  a  higher 
state  of  oxidation  and  form  K4FeCy6,  thus: 

2K3FeCy6  +  2KOH  -f  RO  =  2K4FeCy6  -I-  RO2  +  H2O. 

5.  Alkaline    peroxides    are    decomposed    with    evolution    of 
oxygen,  thus: 

KsFeCye  +  K2O2  +  H2O  =  K4FeCyb  +  KOH  +  O2. 

6.  When   alkalis   are   boiled   with   concentrated   ferricyanide 
solutions,  Fe2O3  is  precipitated  and  ferrocyanide,  cyanide,  and 
(CN)  2  produced. 

Ammonia  forms  ferrocyanides  of  K  and  NH4,  and  evolves  N. 
Mercuric  oxide  gives  HgCy2  and  Fe203: 

K3FeCy6  +  3HgO  +  3H2O  =  3HgCy2  +  3KOH  +  Fe(OH)3. 

7.  A  mixture  of  KCy  and  K3FeCy6  acts  as  a  solvent  of  gold  or 
silver  without  intervention  of  oxygen: 

K3FeCy6  +  2KCy  +  Au  =  K4FeCy«  +  KAuCy2. 

8.  Decomposed  by  chlorine  or  bromine,  forming  first  the  haloid 


92  THE  CYANIDE  HANDBOOK 

cyanogen  compounds  (CNC1  and  CNBr)  and  HCy;  on  continued 
boiling  various  ferrosoferric  ferricy  anides  are  formed. 

9.  Potassium  iodide  forms  an  unstable  compound  which 
readily  breaks  up  into  I  and  K4FeCye. 

10.  Boiling   HC1   forms   KC1,    FeCl3   and    "Turnbull's   blue/' 
Fe3  (FeCy6)2. 

11.  Evaporation  with  nitric  acid  yields  potassium  nitroprusside 
(K2FeCy5NO)  and  KNO3. 

Hydrogen  Ferri cyanide  (H3FeCy6) : 

Hydroferricyanic  Acid.  —  Prepared  by  action  of  H2S04  on  lead 
ferricyanide,  or  by  adding  cold  concentrated  K3FeCy6  to  2  to  3 
times  its  volume  of  concentrated  HC1  and  filtering.  Lustrous 
brownish-green  needles.  Very  soluble  in  water  or  alcohol.  Decom- 
poses in  air,  giving  HCy  and  a  blue  residue. 

Ferricyanides  of  Copper: 

Cuprous  Ferricyanide  (Cu3(FeCy6)  or  Cu6(FeCy6)2). — brown- 
ish-red precipitate,  obtained  by  adding  a  solution  of  Cu2Cl2  in  HC1 
to  K3FeCy6.  Soluble  in  NH3  but  not  in  NH4  salts. 

Cupric  Ferricyanide  (Cu3(FeCy6)2).  —  Yellowish  precipitate, 
obtained  by  adding  a  cupric  salt  to  K3FeCy6.  Probably  contains 
K.  Soluble  in  NH3  and  in  NH4  salts. 

Ferricyanides  of  Iron: 

Ferrous  Ferricyanide  (Turnbull's  Blue:  Fe3(FeCy6)2).  —  Pre- 
pared by  adding  K3FeCy6  or,  better,  H3FeCy6  to  a  ferrous  salt, 
and,  after  digesting  for  some  time,  washing  the  precipitate  with 
hot  water.  Also  prepared  by  partial  oxidation  of  ferrous  ferro- 
cyanide,  Fe2FeCy6: 

2K3FeCyf)  +  3FeSO4  =  Fe3(FeCy6)2  +  3K2SO4. 
2Fe2FeCy6  +  O  -  FeO  +  Fe3(FeCy6)2. 

A  deep  blue  powder,  with  a  tinge  of  copper-red.  Insoluble  in 
water,  alcohol,  and  dilute  acids.  Soluble  in  oxalic  acid.  Cannot 
be  dehydrated  without  decomposition.  Exposed  to  moist  air,  it 
yields  Prussian  blue  and  ferric  oxide : 

6Fe3(FeCy6)2  +  O3  =  4Fe4(FeCy6)3  +  Fe2O3. 

Decomposed  by  alkalis,  alkaline  carbonates,  and  ammonia, 
giving  a  ferricyanide  and  Fe3O4. 

Ferrosoferric  Ferricyanide  (Prussian  Green ;  Pelouze's  Green : 
Fe7(FeCye)6).  --  A  green  precipitate,  obtained  by  passing  Cl 
into  K8FeCy,  and  boiling,  then  washing  the  residue  with  con- 


COMPLEX   METALLIC   CYANIDES  93 

centrated  boiling  HC1.  Changes  to  Prussian  blue  on  contact 
with  air. 

A  black  ferrosoferric  ferricyanide  Fe5  (FeCy6)4?  is  formed  by 
acting  on  K3FeCy6  with  Br. 

Potassium  Ferrous  Ferricyanide  (Soluble  Prussian  Blue: 
FeK  •  FeCy6). — Obtained  by  mixing  solutions  of  FeCl3  and  K4FeCy6 
in  equivalent  proportions,  stirring,  and  at  once  washing  with  cold 
water.  Also  by  action  of  pure  FeSO4  on  K3FeCy6  in  absence  of  air. 
When  dried  in  vacuo  it  has  the  composition  4  (FeK  •  FeCy6)  7H2O. 

A  blue  solid,  soluble  in  cold  water.  Solution  decomposed  by 
boiling,  giving  a  yellowish  precipitate;  on  adding  acids  or  metallic 
salts,  a  blue  precipitate.  Alkalis  and  ammonia  give  Fe(OH)3 
and  a  ferrocyanide.  Ferric  salts  give  Prussian  blue.  Ferrous  salts 
give  Turnbull's  blue. 

Ferricyanide  of  Silver  (Ag3FeCy6).  —  A  reddish-yellow  precipi- 
tate obtained  by  adding  K3FeCy6  to  AgNO3.  Acted  on  by  ammo- 
nia, forming  a  reddish  double  salt,  which  is  soluble  in  excess  of 
ammonia. 

(c)     PERFERRICYANIDES  (M2FeCy6) 

When  K4FeCy6  solution  is  heated  with  iodine  a  greenish-brown 
liquid  is  formed,  from  which  alcohol  precipitates  a  crystalline 
salt,  which  appears  to  be  K2FeCy6.  It  can  be  better  prepared 
by  acting  on  K4FeCy6  with  HC1  and  KC1O3,  neutralizing,  and 
precipitating  with  alcohol.  Nearly  black.  Dissolves  to  a  deep 
violet  solution.  Gives  green  precipitates  with  many  metallic 
salts.  Very  unstable.  Acts  as  a  powerful  oxidizer. 

(d)     NITROPRUSSIDES  (M2FeCy5(NO) ) 

Formation.  —  These  compounds  are  formed  by  acting  on  alkali, 
ferrocyanides,  or  ferricyanides  with  HNO3.  Two  parts  powdered 
K4FeCy6,  5  parts  HNO3,  and  5  parts  water  are  warmed  on  a  water- 
bath.  A  coffee-colored  liquid  is  formed  which  gives  off  HCy,  Cy, 
N,  and  C02.  When  the  liquid  gives  a  dark-green  or  slate-colored 
precipitate  with  a  ferrous  salt  (instead  of  blue),  the  reaction  is 
complete.  After  cooling  and  filtering,  the  liquid  is  neutralized 
with  an  alkali,  again  filtered,  and  evaporated  till  the  alkaline 
nitroprusside  formed  crystallizes. 

They  are  formed  also  by  the  action  of  nitrites  on  ferrocyanides, 
or  on  a  boiling  mixture  of  FeCl3  and  KCy. 


94 


THE  CYANIDE   HANDBOOK 


General  Properties.  — The  alkaline  nitroprussides  are  soluble; 
also  those  of  the  alkaline  earths.  Most  others  are  insoluble. 
Generally  colored. 

CHARACTERISTIC  NITROPRUSSIDES 


Metal 

Color  of  Salt 

Remarks 

NH4                      .... 

Very  Unstable 

Ba 

Dark  red 

Very  Soluble 

Ca 

Very  Soluble 

H          

Dark  red 

Deliquescent 

K                           .... 

Dark  red 

Deliquescent 

Na 

Ruby-red 

Non-deliquescent 

Cu  

Greenish 

Insoluble 

Fe"    

Yellowish  pink 

Insoluble 

Ag 

Flesh-colored 

Insoluble 

Zn  

Yellow-rose 

Insoluble 

General  Reactions.  —  1.  Solutions  of  alkali  nitroprussides  give 
a  deep,  brilliant  purple  color  with  alkali  sulphides.  The  color  soon 
fades/  but  is  often  used  as  a  characteristic  test  for  sulphides  in 
solution. 

2.  Aqueous  solutions  decompose  on  heating  or  exposure  to 
light,  giving  a  blue  precipitate. 

3.  When   boiled   with    alkalis,    Fe(OH)3   is    precipitated,    N 
evolved,  and  a  nitrite  and  ferrocyanide  formed. 

4.  H2S  precipitates  Prussian  blue,  leaving  a  ferrocyanide  in 
solution. 

5.  Soluble  nitroprussides  act  as  powerful  oxidizing  agents. 

6.  KMnO4  forms  NaN03  and  a  ferricyanide. 

COMPOUNDS  CONTAINING  A  METAL  ANALOGOUS  TO  IRON,  FORMING 

A  COMPLEX  RADICAL  WITH  CYANOGEN 
The  chief  classes  of  these  compounds  are: 
Chromocyanides    (M4CrCy6) 
Chromicyanides     (M3CrCy6) 
Cobaltocyanides    (M4CoCy6:  unstable) 
Cobalticyanides     (M3CoCy6) 
Manganocyanides(M4MnCy6) 
Manganicyanides  (M3MnCy6) . 

JThe  products  of  decomposition  are  ferrocyanide,  thiocyanate,  nitrite,  sulphur, 
and  ferric  oxide. 


COMPLEX   METALLIC   CYANIDES  95 

The  chromo-,  cobalto-,  and  mangano-cyanides  (corresponding 
to  ferrocyanides)  are  obtained  by  acting  on  the  salts  of  the  lower 
oxide  of  the  respective  metals  with  strong  solutions  of  KCy. 

The  chromi-,  cobalti-,  and  mahgani-cyanides  are  obtained  by 
oxidizing  the  above  compounds,  or  by  acting  on  the  higher  oxides 
or  salt  of  the  respective  metals  with  KCy. 

Some  of  the  acids  belonging  to  this  series,  namely,  H4CrCy6, 
H4CoCy6,  H3CoCy6,  and  H4MnCy6,  have  been  prepared. 

It  has  been  suggested  that  mixtures  of  KCy  with  cobalti- 
cyanides  or  manganicyanides  might  be  used  as  gold  solvents. 

(B)    METALLIC  COMPOUNDS  OF  RADICALS  IN  WHICH  CYANOGEN  is 
COMBINED  WITH  OXYGEN  OR  A  SIMILAR  ELEMENT. 

A  number  of  substances  are  known  in  which  cyanogen  appears 
to  form  part  of  a  negative  radical,  in  which  it  is  intimately  united 
with  oxygen  or  another  element  (S,  Se)  of  the  oxygen  group. 

These  compounds  have  the  general  formula 

(MR"CN)x, 

where  M  is  a  +  metal  or  group,  and  R"  an  element  (O,  S,  or  Se) 
forming  part  of  a  negative  radical  containing  C  and  N  in  the  pro- 
portions to  form  cyanogen. 

Since  we  may  suppose  the  element  R"  to  be  directly  united 
either  with  the  C  or  with  the  N  of  the  cyanogen,  we  have  two 
classes  of  isomeric  compounds,  corresponding  with  the  formulas 

XM  -  R"  -  C  =  N'"  and  M  -  R"  -  Nv  =  C,  respectively. 

The  latter  are  distinguished  by  the  prefix  "iso." 

Compounds  of  the  type  (MRCN)x  show  a  great  tendency  to 
polymerize,  and  different  classes  of  bodies  are  known  in  which 
x  =  1,  2,  and  3,  respectively. 

Different  theories  have  been  advanced  to  explain  their  con- 
stitution, which  need  not  concern  us  here,  and  innumerable  organic 
derivatives  have  been  described,  often  of  great  complexity,  in 
which  M  is  a  positive  radical  of  the  "alky!"  type  (e.g.,  CH3, 
C2H5,C6H5,  etc). 

The  most  important  substances  for  our  purpose  fall  under 
the  following  groups: 

1  Other  arrangements,  e.g.,  M  -  C  =  N  =  R"  and  M  -  N  =  C  =  R",  are  also 
possible,  and  may  occur  in  certain  compounds. 


96  THE  CYANIDE  HANDBOOK 

Cyanates,  MOCN.  Isocyanates,  MONO. 

Fulminates,  (MOCN)2.         Isodicyanates,  (MONC)2. 
Cyanurates,  (MOCN)3.         Isocyanurates,  (MONC)3. 
Thiocyanates,  MSCN. 
Dithiocyanates,  (MSCN)2. 
Thiocyanurates,  (MSCN)3. 
Selenocyanates,  MSeCN. 

CYANATES  (MOCN) 

Cyanic  Acid  (HOCN).  —  This  acid  is  only  formed  in  small 
quantity  by  decomposing  cyanates  by  stronger  acids,  as  it  im- 
mediately undergoes  further  decomposition.  It  may  be  made 
by  the  action  of  heat  on  its  polymer,  cyanuric  acid  (HOCN)3,  or 
by  dehydrating  urea  (with  phosphorus  pentoxide),  or  by  passing 
dry  HC1  over  dry  AgCNO. 

It  is  a  thin,  colorless  liquid  which  reddens  litmus  and  has  a 
pungent  odor  resembling  acetic  acid.  It  excites  tears,  and  raises 
blisters  on  the  skin.  Soluble  without  decomposition  in  ice-cold 
water.  Readily  polymerizes.  It  is  decomposed  by  water  as 
follows:  HOCN  +  H2O  -  NH3  +  CO2. 

Metallic  Cyanates:  General  Methods  of  Formation.  —  1.  By 
fusing  alkaline  cyanides  or  ferrocyanides  with  easily-reduced 
oxides,  such  as  Pb02,  or  with  oxidizing  agents  (nitrates,  bichro- 
mates, etc.)  :  MCN  +  Q  =  MQCN 

2.  By  passing  cyanogen  into  a  solution  of  an  alkali  or  alkaline 
earth;  e.g..  (CN)a  +  2KOH  =  KCN  +  KOCN 


3.  By  heating  alkaline  carbonates  to  low  redness  in  an  atmos- 
phere of  cyanogen,  or  with  mercuric  cyanide: 

M2CO3  +  (CN)2  =  2MOCN  +  CO. 

4.  By  electrolysis  of  soluble  cyanides. 

General  Properties  and  Reactions.  —  1.  Most  metallic  cyanates 
are  soluble  in  water;  those  of  Ag,  Cu,  Pb,  and  Hg  are  only  slightly 
soluble. 

2.  Alkali  cyanates  are  not  decomposed  by  heating  to  dull 
redness  in  dry  air.  In  moist  air  they  give  carbonates  of  am- 
monium and  the  alkali: 

2MOCN  +  4H2O  =  M2CO3  +  (NH4)2CO3. 


COMPLEX  METALLIC    CYANIDES  97 

Cyanates  of  the  heavy  metals  are  decomposed  by  heat  into 
CO2  and  a  cyanide  of  the  metal: 

2M'(OCN),  =  M*(CN)»+M'+2CQ»+Ni 

3.  Easily  decomposed  in  solution  by  water  into  carbonates 
and  ammonium  salt  (see  above);    or  by  dilute  acids  into  CO2, 
an  ammonium  salt  of  the  acid,  and  a  metallic  salt  of  the  acid; 

e'9'>1  MOCN  +  2HC1  +  H2O  =  MCI  +  NH4C1  +  CO2. 

4.  Reduced   to   cyanides   by  heating  with   certain   reducing 
agents  —  H,  C,  K,  or  Fe. 

5.  Melted  with  sulphur,  they  give  sulphides,  sulphates,  and 
thiocyanates. 

6.  Sodium  amalgam  reacts  with  neutral  cyanates  to  produce 
formamide  (HCONH2). 

'7.  Certain  metallic  cyanates  are  obtained  by  acting  on  salts 
of  the  required  metal  with  alkaline  cyanates,  and  crystallizing 
from  alcohol. 

8.  Silver  Cyanate:  Silver  salts  give  a  white  precipitate 
(perhaps  AgONC),  insoluble  in  cold  water,  soluble  in  boiling 
water;  dissolved  and  decomposed  by  dilute  nitric  acid: 

AgOCN  +  2HNO3  +  H2O  =  AgNO3  +  CO2  +  NH4NO3. 

Silver  cyanate  is  decomposed  by  heat  into  Ag  mixed  with  C 
and  some  N  and  CO2.  It  is  soluble  in  NH3,  giving  a  double  com- 
pound which  loses  NH3  in  the  air. 

Potassium  Cyanate  (KOCN) :  Preparation.  —  By  the  general 
methods  given  above;  best  as  follows:  4  parts  K4FeCy6  and  3 
parts  K2Cr207,  both  dry  and  pulverized,  are  mixed,  and  the 
mixture  heated,  a  little  at  a  time,  till  it  blackens.  After  cooling 
it  is  extracted  with  boiling  alcohol,  and  KCNO  crystallized  out 
and  dried  in  vacuo. 

Properties.  —  Small,  colorless,  odorless  laminae  resembling 
KC103.  Soluble  in  water;  fairly  soluble  in  boiling  hydrated 
alcohol.  Insoluble  in  absolute  alcohol. 

1.  According  to  some  writers,2  the  salt  present  in  commercial 
cyanide  is  an  isocyanate  (presumably  KONG  or  KNCO),  which 
is  gradually  transformed  in  solution  into  the  normal  cyanate 

1  Concentrated  HCl  or  dilute  H2SO4  give  a  certain  amount  of  HOCN. 

2  Bettel  and  Feldtmann,  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa," 
I,  273. 


98  THE  CYANIDE  HANDBOOK 

(KOCN),   which  latter  has  no   action   on   silver  nitrate.     This, 
however,  is  denied  by  other  authorities,1  who  maintain  that  the 
decomposition  taking  place  is  merely  the  gradual  formation  of 
ammonium  and  potassium  carbonate,  referred  to  above: 
2KOCN  +  4H20  =  K2C03  +  (NH4)2CO3. 

2.  When  BaCl2  is  added  to  a  solution  of  KOCN,  it  gives  at 
first  no  precipitate;    but  on  boiling,  barium  carbonate  is  thrown 

down:  (a)  2KCNO  +  BaCl2  -  Ba(CNO)2  +  2KC1. 

(6)  Ba(CNO)2  +  4H2O  =  BaCO3  +  (NH4)2CO3. 

3.  A  solution  of  cobalt  acetate  gives,  with  potassium  cyanate, 
dark  blue  quadratic  crystals  of  a  double  cyanate  (CoK2(CNO)4). 
This  reaction  has  been  proposed  as  a  test  for  cyanates. 

FULMINATES  (MOCN)2 

These  are  unstable,  often  explosive  substances,  formed  by 
the  action  of  alcohol  on  metallic  nitrates.  The  acid  itself  has 
not  been  isolated.  The  most  important  are  those  of  silver, 
mercury,  and  gold. 

Mercuric  fulminate  (Hg(OCN)2).  —  Used  in  the  manufacture 
of  percussion  caps.  It  is  prepared  by  dissolving  mercury  in  cold 
nitric  acid,  and  pouring  the  solution  into  90  to  92  per  cent,  alcohol. 
The  salt  deposits  and  is  recrystallized  from  water.  Crystallizes 
from  alcohol  in  octahedra;  from  water  in  needles.  Very  slightly 
soluble  in  cold  water,  more  soluble  in  hot  water. 

Explodes  by  heat,  friction,  percussion,  or  treatment  with 
H2SO4,  yielding  Hg,  N,  and  CO.  When  heated  with  water  it 
polymerizes  to  fulminurate.  Forms  double  salts  with  cyanides. 

CYANURATES  (MOCN)3 

Cyanuric  acid  is  a  product  of  the  decomposition  of  urea  by 
heat:  3CO(NH2)2  =  (HOCN)3  +  3NH3. 

It  is  precipitated,  on  dissolving  the  residue  and  diluting  with 
water,  in  colorless,  oblique,  rhombic  prisms  (with  2H20).  Ef- 
floresces. Converted  into  anhydrous  octahedra  at  100°-120°  C. 
Slightly  soluble  in  cold  water,  more  soluble  in  hot  water.  Soluble 
in  hot  acids  without  decomposition.  Heated  in  a  closed  tube,  it 
gives  cyanic  acid:  (HCNQ)3  =  3HOCN 

1  Victor,  in  "Zeit.  fur  anal.  Chem./'  XL,  462-465. 


COMPLEX   METALLIC    CYANIDES  99 

When  dissolved  in  NH3  it  gives  a  fine  pink  precipitate  with 
ammonio-sulphate  of  copper. 
PC15  forms  (CNC1)3. 

Cyanurates  are  precipitated  by  Ba  salts  but  not  by  Ca  salts. 
They  may  occur  sometimes  in  working  cyanide  solutions.  The 
following  formula  has  been  suggested  as  representing  their  con- 
stitution: 

OH 
I 
C 


Only  organic  derivatives  of  the  isodicyanates  and  isocyanurates 
are  known. 

THIOCYANATES  (MSCN) 

General  Methods  of  Formation.  —  1.  By  fusion  of  cyanides 
or  ferrocyanides  with  sulphur  or  with  alkaline  sulphides  or  poly- 
sulphides,  or  thiosulphates. 

2.  By  the  action  of  alkaline  polysulphides  on  cyanides  in 
aqueous  solution. 

Properties.  —  Soluble,  often  deliquescent  salts.  The  thio- 
cyanates  of  copper  (cuprous),  lead,  mercury,  and  silver  are  white 
or  yellowish  insoluble  salts. 

General  Reactions.  —  1.  Solutions  give  a  deep-red  color  with 
ferric  salts:  3KCNS  +  FeCl3  =  3KC1  +  Fe(SCN)3. 

2.  Alkali  thiocyanates  are  decomposed  by  heat  in  presence 
of  air,  giving  a  sulphate  and  cyanate  of  the  metal,  and  evolving 
SO2.     Thiocyanates  of  the  heavy  metals  give  a  sulphide,  S,  CS2, 
and  finally  (CN)2  and  N. 

3.  Oxidizing  agents  form  sulphates:  e.g., 

5KSCN  +  6KMnO4  +  12H2SO4  =  11KHSO4  +  6MnSO4  +  5HCN  +  4H2O. 

4.  Copper  salts  in  presence  of  a  reducing  agent  precipitate 
white  cuprous  thiocyanate,  insoluble  in  water  and  dilute  acids: 

2KCNS  +  2CuSO4  4-  Na2SO3  +  H2O  =  Cu2(SCN)2  -I-  KzSO*  +  2NaHSO4, 

5.  Silver  salts  give  a  white  curdy  precipitate  of  silver  thio- 
cyanate: KCNS  +  AgNO3  =  AgSCN  +  KNOa. 


100  THE  CYANIDE  HANDBOOK 

AgSCN  is  insoluble  in  water  and  dilute  acids,  soluble  in  am- 
monia, alkaline  cyanides,  and  thiocyanates,  and  also  in  mercu- 
rous  nitrate.  Forms  soluble  double  thiocyanates  with  KSCN. 
(NH4)SCN,  etc. 

6.  Salts  of  mercury  give  white  precipitates;  the  mercurous 
salt  is  unstable  and  readily  decomposes  with  separation  of  Hg. 
Mercuric  thiocyanate  swells  greatly  on  heating,  giving  off  Hg,  N, 
and  CS2. 

Ammonium  Thiocyanate  (NH4  •  SCN) :  Preparation.  —  1.  By 
digesting  HCN  with  ammonium  polysulphide  (S  dissolved  in 
(NH4)2S).  On  boiling,  S  separates,  and  the  filtrate  contains 
NH4SCN. 

2.  By  decomposing  cupric  thiocyanate  with  NH4  •  HS,  filter- 
ing and  evaporating. 

3.  By   evaporating   a   mixture    of    ammonia   with    alcoholic 
solution  of  CS2. 

4.  By  heating  ammonium  sulphate  with  carbon  and  sulphur: 

(NH4)2SO4  +  C  +  S  =  NH4SCN  +  SO2  +  2H2O. 

Properties.  —  Large,  white,  deliquescent  plates,  very  soluble 
in  water  and  alcohol.  Melts  at  159°  C.  Dissolves  in  water  with 
great  absorption  of  heat. 

Reactions.  —  1.  Heated  to  180°-190°  C.,  it  gives  off  CS2,  H2S, 
and  NH3. 

2.  Heated  for  some  time  nearly  to  melting-point,  it  is  con- 
verted into  its  isomer,  thiourea  (CS(NH2)2). 

3.  Forms  double  salts  with  HgCy2  and  with  various  thio- 
cyanates. 

Potassium  Thiocyanate  (KSCN) :  Formation.  —  1.  By  fusing 
potassium  sulphide  with  ferrocyanide,  K2S203  is  first  formed;  at 
a  higher  temperature  this  reacts  to  form  KSCN. 

2.  By  acting  on  ammonium  thiocyanate  with  potassium  sul- 
phide or  potash  at  high  temperature: 

2NH4SCN  +  K2S  =  2KSCN  +  (NH4)2S. 
NH4SCN  +  KOH  =  KSCN  +  NH3  +  H2O. 

Properties.  —  Long,  white,  striated  prisms  resembling  niter. 
Very  soluble  in  water,  with  great  absorption  of  heat.  MeJte  at 
161.2°  C.  Non-poisonous. 

Reactions.  —  1.    On  melting,  the  salt  turns  green,  then  indigo, 


COMPLEX   METALLIC    CYANIDES  101 

but  becomes  white  again  on  cooling.     Heated  in  moist  air,  it 
gives  CO2,  NH3,  and  K2S. 

2.  Aqueous  solution  slowly  decomposes  (rapidly  on  boiling), 
evolving  ammonia,: 

2KSCN  +  4H20  =  K2S  +  (NH4)2S  +  2CO2. 

3.  Heated  with  iron,  it  forms  FeS,  K2S,  and  K4FeCye. 

4.  On  electrolysis,  it  gives  H2SO4,  SO2,  HCN,  and  S. 

5.  HC1  gas  reacts  violently  with  molten  KSCN,  forming  HCN, 
CS2,  and  NH4C1. 

6.  Concentrated  nitric  acid  forms  "  pseudo-sulphocyanogen " 
(C3N3HS3).     The  same  compound  is  formed  by  action  of  Cl  on 
concentrated  solution  of  KSCN.     With  excess  of  Cl  the  products 
are  NH4C1,  (NH4)2SO4,  and  CO2.     Cl,  passed  into  molten  KSCN, 
gives  S2C12  and  (CNC1)3. 

7.  Heated  gently  with  PC15,  it  gives  KC1,  CNC1,  and  PSC13. 

8.  Forms  double  salts  with  HgCy2  and  HgI2. 
Thiocyanates  of  Gold  and  Potassium: 

Auro  potassic  Thiocyanate  (KAu(SCN)2).  —  When  auric  chlo- 
ride (AuCl3)  is  added  drop  by  drop  to  KSCN  at  80°  as  long  as  the 
precipitate  dissolves,  and  the  liquid  is  evaporated  and  crystallized, 
straw-yellow  prisms  are  obtained,  melting  at  100°  C.  Decom- 
posed by  heat  into  Au,  S,  CS2,  and  KSCN.  Solution  blackens 
in  light.  Gives  precipitates  with  various  salt  solutions.  NH3 
precipitates  NH3  •  AuSCN. 

Auripotassic  Thiocyanate  (KAu(SCN)4).  —  When  AuCl3  is 
added  to  excess  of  KSCN  in  the  cold,  this  substance  is  formed, 
which  crystallizes  from  warm  water  in  orange-red  needles.  Soluble 
in  water,  alcohol,  and  ether.  Forms  double  compounds. 

An  analogous  aurisodic  thiocyanate,  NaAu(SCN)4,  is  also 
known. 


SECTION   IV 

CHEMISTRY  OF  THE  DISSOLVING  PROCESS 

Necessity  of  Oxygen  in  Ordinary  Cyanide  Process.  —  The  re- 
searches of  Bagration,  Eisner,  Faraday,  and  latterly  of  J.  S. 
Maclaurin,1  have  demonstrated  that  under  ordinary  circumstances 
the  presence  of  oxygen  is  necessary  for  the  solution  of  metallic 
gold  and  silver  in  cyanide  solutions.  The  reaction  may  in  fact 
be  expressed  in  the  form  frequently  quoted  as  "  Eisner's  equation," 
though  not  originally  due  to  him : 

2Au  +  4KCy  +  O  +  H2O  =  2KAuCy2  +  2KOH. 

Intermediate  Products  of  Reaction.  —  The  correctness  of  this 
equation  as  representing  the  final  result  of  the  reaction  has  been 
abundantly  verified  by  Maclaurin  and  other  investigators,  but 
it  is  quite  possible  that  intermediate  products  are  formed,  so  that 
the  actual  mechanism  of  the  reaction  is  not  so  simple  as  would 
appear  from  the  above.  Bodlander2  states  that  hydrogen  per- 
oxide is  first  produced,  and  that  a  portion  of  this  is  further  de- 
composed, an  additional  amount  of  gold  being  dissolved.  The 
reactions  he  gives  are  as  follows: 

(a)  2Au  +  4KCy  +  2H2O  +  O2  =  2KAuCy2  +  H202  +  2KOH. 
(6)  2Au  +  4KCy  +    H2O2  =  2KAuCy2  +  2KOH. 

It  is  stated  that  H202,  or  some  substance  having  similar  re- 
actions, can  be  detected  in  the  solution.  Bettel,  however,  states 
that  the  intermediate  product  is  potassium  auricyanide,  and 
proposes  the  following: 

(a)  2Au  +  6KCy  +  2H2O  +  O2  =  KAuCy2  +  KAuCy4  +  4KOH. 
(6)  2Au  +  2KCy  +  KAuCy4        =  3KAuCy2. 

The  reactions  in  the  case  of  silver  appear  to  be  precisely 
analogous. 

1  Maclaurin,   "Proc.  Chem.  Soc.,"  CXII,  p.  81;  CXLVI,  pp.  7-8;  CLXVIII, 
p.  149. 

2  Bodlander,  "  Zeit.  fur  angew.  Chem., "   1896,  pp.  583-587. 

102 


CHEMISTRY  OF  THE  DISSOLVING   PROCESS  103 

Use  of  Artificial  Oxidizers.  —  The  necessity  for  oxygen  being 
thus  recognized,  it  seemed  natural  to  suppose  that  the  reaction 
would  be  assisted  and  hastened  by  the  addition  of  substances 
which  would  readily  yield  oxygen  under  the  conditions  of  cyanide 
treatment.  The  advantage,  however,  was  only  apparent  in  a 
few  cases,  namely,  in  those  of  alkaline  peroxides,  ferricyanides, 
and  permanganates.  In  the  case  of  peroxides  the  decomposition 
takes  place  rapidly  in  presence  of  water: 

Na2O2  +  H2O  =  2NaOH  +  O; 

and  consequently  they  are  of  little  use  unless  added  to  dry  ore 
previous  to  cyanide  treatment.  In  the  case  of  ferricyanides, 
the  reaction  is  very  probably  quite  independent  of  oxygen,  as 
already  pointed  out.  The  reaction  with  permanganate  is  some- 
what complicated;  formates,  oxalates,  nitrites,  urea,  and  am- 
monia being  among  the  products  (in  alkaline  solutions),  and  it 
does  not  appear  to  be  known  with  any  certainty  how  permanga- 
nates act  in  aiding  the  solution  of  gold.  If  manganicyanides  are 
formed,  the  reaction  is  probably  analogous  to  that  of  ferricyanides. 
Solutions  completely  deprived  of  oxygen  were  found  to  have  no 
solvent  effect  whatever;  and  the  addition  to  such  solutions  of 
chlorates,  perchlorates,  chromates,  bichromates,  nitrates,  nitrites, 
or  bleaching  powder  had  no  effect,  and  did  not  bring  about  solu- 
tion of  the  gold.1 

Solution  of  Metals  in  Cyanide  Independently  of  Oxygen.  —  We 
have  already  noted  several  types  of  reaction  in  which  gold  is 
dissolved  (usually  by  the  interaction  of  two  different  cyanogen 
compounds,  one  of  them  being  a  simple  alkali  cyanide),  in  which 
oxygen  plays  no  part.  We  may  here  briefly  enumerate  the  fol- 
lowing cases,  some  of  which  have  been  already  referred  to: 

(1)  The  haloid  compounds  of  cyanogen;  e.g., 

3KCy  +  CyBr  +  2Au  =  2KAuCy2  +  KBr. 

(2)  Double  cyanides  of  copper  and  alkali  metal;  e.g., 

CU2Cy2  -  4KCy. 

(3)  Cuprammonium  cyanides  of  the  type 

x(NH3)  -y(CuCy2)  -z(Cu2Cy2). 
These  readily  decompose  with  formation  of  the  insoluble  salt 

1  Bettel  and  Marais;   quoted  by  T.  K.  Rose,  "Metallurgy  of  Gold,"  4th  ed.,  p.  380. 


104  THE  CYANIDE  HANDBOOK 

4NH3  •  CuCy2  •  2Cu2Cy2  and  liberation  of  cyanogen,  which  at  the 
moment  of  formation  attacks  gold  in  presence  of  KCy: 

KCy  +  Cy  +  Au  =  KAuCy2. 

(4)  Double  cyanides  of  mercury  and  alkalis: 

K2HgCy4  +  2Au  =  2KAuCy2  +  Hg. 

(5)  Double  cyanides  of  zinc  and  alkalis.     [These  are  stated 
to  be  solvents  of  gold  by  themselves,  but  it  is  evident  that  no 
reaction  analogous  to  No.  4,  above,  can  take  place.     It  seems  more 
probable  that  the  molecule  breaks  up  in  solution: 

K2ZnCy4  =  2KCy  +  ZnCy2. 

and  that  the  dissolving  of  gold  is  due  to  the  ordinary  reaction  of 
KCy  in  presence  of  O  and  H2O.] 

(6)  Ferricyanides  and  analogous  compounds: 

2KCy  +  K3FeCy6  +  Au    =K4FeCyG   +  KAuCy2. 
2KCy  +  KsMnCye  +  Au  =  K4MnCy6  +  KAuCy2. 


In  practice,  these  aids  to  solution  have  had  only  a  limited 
application,  but  arrangements  for  bringing  air  into  intimate  con- 
tact with  the  material  undergoing  treatment,  and  with  the  cyanide 
solution,  have  sometimes  proved  of  great  value.  In  such  cases 
it  may  be  doubted  whether  the  oxygen  directly  aids  the  solution 
of  gold,  or  whether  the  beneficial  action  is  not  rather  due  to  the 
destruction  of  cyanicides,  or  of  precipitants  of  gold,  present  in  the 
material  to  be  treated.  According  to  H.  F.  Julian,1  free  oxygen 
plays  no  primary  part  in  the  dissolution  of  gold  by  cyanide,  but, 
on  the  contrary,  exerts  a  retarding  influence.  He  ascribes  the 
solvent  action  of  cyanide  (as  did  Faraday)  to  the  formation  of 
local  voltaic  circuits.  "These,  in  the  first  instance,  deposit 
hydrogen  and  oxygen,  which  it  may  be  assumed  become  occluded 
at  their  respective  electrodes  until  the  systems  are  in  equilib- 
rium." When  this  condition  is  reached,  less  expenditure  of  energy 
is  required  to  remove  Cy  from  the  solution  than  to  occlude  a  further 
quantity  of  O,  and  accordingly  AuCy  is  formed  and  is  deposited 
in  films.  This  compound  has  a  high  potential,  and  acts  as  an 
electrode,  forming  a  couple  with  the  uncombined  gold.  The 
AuCy  then  dissolves  in  the  excess  of  KCy,  "  as  one  salt  dissolves 

1  Julian,  "Brit.  Assoc.  Reports,"  South  Africa,  1905,  p.  369. 


CHEMISTRY  OF  THE   DISSOLVING   PROCESS  105 

in  the  solution  of  another."  When  the  solution  contains  dis- 
solved oxygen,  this  aids  in  a  secondary  manner  by  oxidizing  the 
occluded  hydrogen  produced  by  the  local  voltaic  currents,  and 
thus  upsetting  the  equilibrium. 

Factors  that  Influence  Solubility  of  Gold  and  Silver.  —  What- 
ever may  be  the  correct  theoretical  explanation  of  the  reaction, 
it  has  been  observed  in  practice  that  certain  factors  exert  an 
influence  on  the  rate  of  solution  of  the  precious  metals  in  cyanide. 
The  most  important  of  these  are: 

(1)  Degree  of  concentration  of  the  solution. 

(2)  Temperature. 

(3)  Presence  or  absence  of  "Cyanicides,"  i.e.,  of  substances 
other  than  the  precious  metals,  capable  of  decomposing  or  com- 
bining with  cyanides. 

(4)  Amount  of  "available  oxygen,"  either  free  or  in  some 
easily  decomposed  compound. 

(5)  Physical  condition  of  the  surfaces  of  metallic  gold  and 
silver  in  contact  with  the  solution. 

(6)  Area  of  metal  exposed  in  proportion  to  weight. 

(7)  Relative  masses  of  solvent,  and  matter  undergoing  treat- 
ment in  contact  with  it. 

Influence  of  Strength  of  Solution.  —  It  has  been  found  by 
Maclaurin  *  that,  other  things  being  equal,  both  gold  and  silver 
dissolve  most  rapidly  in  solutions  of  a  strength  corresponding  to 
0.25  per  cent.  KCy  (i.e.,  0.10  per  cent.  Cy).  The  rate  of  solution 
falls  off  gradually  above  or  below  this  strength,  but  is  nearly 
constant  between -0.1  per  cent.,  and  0.25  per  cent.  KCy.  His 
experiments  show  that  the  rate  of  solution  of  silver  is  about  two- 
thirds  that  of  •  gold,  but  otherwise  the  phenomena  are  similar. 
L.  Janin's  experiments,2  however,  show,  for  cement  silver,  a 
maximum  solubility  at  1  per  cent.  KCy.  The  reduced  efficiency 
of  stronger  solutions  has  been  ascribed  to  the  diminished  solu- 
bility of  oxygen  in  strong  KCy.  It  would  seem,  however,  that 

+          + 

the  dissociation  of  cyanide  into  its  ions,  K  (or  Na)  and  CN,  is 
an  essential  condition  to  the  solution  of  gold  or  any  metal  therein. 
Since  this  dissociation  takes  place  the  more  completely,  the  more 
dilute  the  solution,  there  must  be  some  point  of  maximum  effi- 

1  J.  S.  Maclaurin,  "Journ.  Chem.  Soc.,"  LXIII,  731;   LXVII,  199. 
2L.  Janin,  "  Eng.  and  Min.  Journ.,"  Dec.  29,  1888. 


106  THE  CYANIDE  HANDBOOK 

ciency  at  which  the  solution  contains  the  greatest  possible  num- 

4^V'     ber  of  CN  ions  per  unit  volume. 

\^    V  Influence  of  Temperature.  —  It   has   long   been   known   that 

U*     \,*          hot  solutions  dissolve  the  metals  more  rapidly  than  cold  ones, 

and  the  greater  efficiency  of  hot  cyanide  solution  for  dissolving 

gold  was  pointed  out  by  Bagration  in  1843.     Experimental  trials 

with  solutions  heated  to  about   130°  F.  (55°  C.)   have  generally 

shown  a  somewhat  higher  extraction  than  at  the  ordinary  tem- 

/    (.  perature.     In  the  practical  application  of  this  observation,  how- 

f\  ever,  there  are  economic  difficulties,  depending  on  the  cost  of 

raising  large  volumes  of  liquid  to  a  high  temperature;  and  more- 
over, there  is  in  hot  solutions  a  somewhat  rapid  decomposition 
of  cyanide,  as  described  below. 

Influence  of  other  Soluble  Substances:  Electrochemical  Order  of 
Metals  in  Cyanide  Solution:  The  relative  solubilities  of  metals 
in  cyanide  (or  other  solvent)  depend  upon  their  electrochemical 
order  in  that  solvent.  Determinations  of  the  electrochemical 
order  of  metals  in  potassium  cyanide  solution,  under  various 
conditions  of  dilution  and  temperature,  have  been  published 
by  Gore,  Skey,  Christy,  and  others.  Generally  speaking,  the 
order,  from  positive  to  negative,  of  the  ordinary  metals,  is  as 
follows: 

+  Mg  Ag 

Al  Hg 

Zn  Pb 

Cu  Fe 

Au  -  Pt 

Carbon  is  —  to  Pt. 

From  this  table  it  may  be  inferred  that  any  metal  in  the  list 
would  tend  to  dissolve  in  cyanide  more  readily  than  the  metal 
below,  and  would  displace  that  metal  from  solution  and  precipitate 
it;  for  example,  zinc  will  precipitate  Cu,  Au,  or  Ag;  copper  will 
precipitate  Au  or  Ag;  gold  or  silver  will  precipitate  mercury; 
magnesium  or  aluminium  will  precipitate  gold  or  silver  more 
readily  than  will  zinc. 

The  solubility,  and  in  some  cases  the  order,  is  affected  by 
differences  of  concentration  and  temperature. 

Experiments  on  the  electromotive  force  of  minerals  in  cyanide 


CHEMISTRY  OF   THE   DISSOLVING   PROCESS  107 

solutions  *  show  that  most  minerals  are  electronegative  to  metallic 
gold,  so  that  gold  tends  to  dissolve  in  preference  to  such  minerals. 

In  ore  treatment,  it  is  generally  found  that  the  percentage 
of  gold  extracted  is  higher  than  that  of  silver,  but  this  may  easily 
be  accounted  for  when  it  is  considered  that  the  actual  weight 
of  silver  present  in  an  ore  is  generally  much  greater  than  that  of 
gold,  and  that  the  silver  is  largely  present,  not  as  metal,  but  as 
a  compound  such  as  Ag2S,  only  slightly  soluble  in  KCy. 

Selective  Action  of  Dilute  Solutions.  —  It  is  claimed  that  dilute 
cyanide  solutions  have  a  "selective  action"  for  gold  and  silver 
in  preference  to  base  metals.  In  the  case  of  the  majority  of  ores, 
the  actual  experimental  facts  may  be  stated  as  follows: 

(1)  It  is  not  usually  the  case  that  the  actual  amount  of  base 
metal  dissolved  is  less  than  that  of  precious  metal;  but  whether 
the  solution  be  strong  or  weak,  the  amount  of  base  metal  dissolved 
relatively  to  the  total  quantity  of  base  metal  present  is  less  than 
the  quantity  of  precious  metal  dissolved  relatively  to  the  total 
quantity  of  precious  metal  present. 

(2)  The  weight  of  precious  metal  dissolved  per  unit  of  base 
metal  or  compound  dissolved  in  a  given  case  is  the  greater  the 
more  dilute  the  solution.     In  all  actual  cases,  the  precious  and 
base  metals  are  dissolved  simultaneously,  but  the  rate  of  solu- 
tion of  the  precious  metals  is  less  diminished  by  dilution  than 
that  of  the  base  metals. 

These  phenomena  are  nx>t  by  any  means  confined  to  cyanide 
solutions:  the  same  laws  are  observed  in  the  action  of  thiosul- 
phates  on  silver  chloride,  in  ores  which  have  undergone  a  chloridiz- 
ing  roast,  and  in  the  action  of  acids  on  powdered  rock-mixtures 
containing  different  percentages  of  almost  any  two  or  more  in- 
gredients soluble  in  the  acid.  In  general  terms,  it  may  be  said 
that  the  ingredient  which  is  present  in  the  smaller  percentage  is 
dissolved  in  the  greater  relative  amount;  the  difference  becoming 
more  marked  the  more  dilute  the  solution. 

Since  the  formation  of  base-metal  compounds  is  the  main 
source  of  consumption  of  cyanide  in  the  treatment  of  most  ores, 
it  follows  that  the  consumption  of  cyanide  may  be  taken,  roughly, 
as  an  index  of  the  amount  of  base  metal  dissolved  in  any  given 
case.  It  is  nearly  always  found  that  the  consumption  of  cyanide 
increases  regularly  as  the  strength  of  the  solution  is  increased, 

>  Christy,  Trans.  A.  I.  M.  E.  (Sept.,  1899),  XXX,  1-83. 


108 


THE  CYANIDE  HANDBOOK 


but  that  the  amount  of  gold  or  silver  dissolved  only  increases 
slightly,  if  at  all,  with  increasing  strength  of  cyanide,  provided 
a  reasonably  sufficient  time  be  given  for  the  action.  The  experi- 
ments by  Mac  Arthur,  quoted  by  Rose,1  illustrate  this  point,  as 
do  also  the  following  tests  by  Caldecott; 2  in  which  charges  of 
34  tons  each,  assaying  originally  100  grains  per  ton,  were  treated 
for  three  days  with  various  strengths  of  solution,  and  subsequently 
water-washed. 


Strength  of 
Cyanide  Used. 
KCy,  Per  Cent. 

Strength  after 
Treatment. 
KCy,  Per  Cent. 

KCy  Consumed. 
Per  Cent. 

Gold  Extracted. 
Per  Cent. 

.041 

.010 

.017 

83 

.110 

.068 

.024 

84 

.373 

.277 

.055 

83 

1.023 

.860 

.095 

85 

3.333 

3.020 

.180 

83 

Many  other  experiments  might  be  quoted  from  which  it  would 
appear  that  while  the  extraction  is  practically  constant,  the  con- 
sumption is  higher  the  greater  the  cyanide  strength. 

Decomposition  of  Cyanide  by  External  Influences.  —  In  its 
early  days,  objections  were  frequently  raised  against  the  practical 
application  of  the  cyanide  process  on  account  of  the  instability 
of  potassium  cyanide  when  exposed  to  atmospheric  influences. 
It  was  urged  that  this  substance  undergoes  spontaneous  decom- 
position, and  that  it  is  rapidly  affected  by  atmospheric  oxygen 
and  carbonic  acid.  A  dilute  solution  of  KCN,  as  already  pointed 

+ 
out,  is  probably  to  a  large  extent  dissociated  into  the  ions  K  and 

CN. 

Hydrolysis.  —  In  addition  to  this,  but  to  a  smaller  extent, 
a  decomposition  known  as  "hydrolysis"  occurs,  as  follows: 

KCy  +  H2O  =  KOH  +  HCy. 

The  HCy  thus  formed  is  continually  volatilized,  and  the  smell  of 
it  is  always  noticeable  over  vessels  containing  a  solution  of  any 
alkali  cyanide. 

The  alkali  cyanides  in  the  solid  state  are  not  stable  unless 


1  "Metallurgy  of  Gold,"  4th  edition,  p.  392. 

2  "Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  I,  294. 


CHEMISTRY  OF  THE  DISSOLVING   PROCESS  109 

perfectly  dry;  sodium  cyanide  is  especially  liable  to  decomposition 
when  existing  as  a  hydrate,  and  reacts  with  water  evolving 
ammonia;  thus:  NaCN  +  2H2O  =  HCO2Na  +  NH3- 


A  similar  decomposition  occurs  with  all  soluble  cyanides  of 
the  alkalis  and  alkaline  earths,  but  much  more  rapidly  in  hot 
solutions,  producing  a  formate  of  the  metal  and  evolving  am- 
monia gas.  The  hydrolytic  decomposition  into  formates  and 
ammonia  is  also  promoted  by  the  presence  of  large  amounts  of 
alkali. 

It  has  been  stated  that  sodium  cyanide  is  less  stable  in  solu- 
tion than  potassium  cyanide  of  corresponding  cyanogen  strength, 
or  than  the  mixed  cyanides  frequently  obtained  as  a  commercial 
product. 

Oxidation.  —  The  cyanides  also,  both  in  the  solid  state  and 
in  solution,  gradually  absorb  oxygen  and  carbonic  acid  from  the 
air;  the  solid  cyanides  are  deliquescent  and  are  gradually  acted 
upon  by  the  moisture  they  absorb  from  the  air.  They  are  ulti- 
mately converted  into  carbonates,  possibly  in  some  cases  with 
formation  of  cyanates  as  intermediate  products,  the  ultimate 
reaction  being: 

2KCN  +  O2  +  4H2O  =  K2CO3  +  (NH^Oa. 

The  oxidation  in  solution  is,  however,  very  slow  under  ordinary 
circumstances,  and  air  or  oxygen  may  be  injected  under  pressure 
into  a  cyanide  solution  for  a  long  time  without  any  appreciable 
oxidation  of  cyanide  taking  place. 

Action  of  Cafbonic  Acid.  —  In  the  absence  of  free  alkali, 
carbonic  acid  decomposes  cyanide;  thus: 

KCN  +  CO2  +  H2O  =  HCN  +  KHCO3. 

This  does  not  take  place,  however,  if  sufficient  caustic  alkali 
(NaOH,  KOH,  Ca(OH)2,  Ba(OH)2)  or  ammonia,  or  alkaline  car- 
bonate (K2CO3  ,  Na2CO3),  be  present  to  neutralize  the  CO2  accord- 
ing to  the  reactions: 

KOH  +  CO2  =  KHCO3. 
-f  CO2  +  H2O  =  2KHCO3. 


Alkali  bicarbonates  afford  no  protection  against  CO2;  as  soon  as 
all  hydrates  and  carbonates  have  been  converted  into  bicarbonates, 
any  further  quantities  of  CO2  entering  the  solution  at  once  de- 
compose the  cyanide.  These  decompositions  are,  however,  of 


110  THE  CYANIDE  HANDBOOK 

less  importance  in  dilute  solutions  than  might  be  supposed,  and 
the  addition  of  a  slight  excess  of  alkali  prevents  the  rapid  evolu- 
tion of  HCy,  even  when  solutions  are  exposed  to  the. air  in  open 
vessels. 

Action  of  Base  Metal  Compounds:  Iron  Compounds.  —  In  the 
treatment  of  ores  a  certain  amount  of  cyanide  is  always  con- 
sumed in  attacking  the  compounds  of  base  metals  contained 
therein.  Of  these  metals  the  commonest  is  iron,  which  occurs 
in  a  variety  of  conditions,  some  of  which  are  unaffected  by  cyanide, 
while  others  are  rapidly  attacked. 

Iron  in  the  form  of  ferric  oxide  is  quite  unaffected  by  cyanides; 
the  same  is  also  probably  true  of  anhydrous  ferrous  oxide  and 
magnetic  oxide.  Ferrous  hydrate,  however,  is  rapidly  acted  upon 
with  formation  of  f errocyanide : 

Fe(OH)2  +  2KCy  =  FeCy2  +  2KOH. 
FeCy2  -f  4KCy  =  K4FeCy6. 

Similarly  with  ferrous  carbonate: 

FeC03  +  6KCy  -  K4FeCy6  +  K2CO3. 

which  reaction  explains  the  efficiency  of  ferrous  carbonate  as  an 
antidote  for  cyanide  poisoning. 

Iron  pyrites  exist  in  ores  in  two  different  crystalline  conditions, 
known  as  "pyrite"  and  "marcasite."  Pyrite,  which  occurs  in 
dense  yellowish  cubical  crystals,  is  only  slowly  acted  on  by  cyanide, 
whereas  marcasite,  which  is  softer,  is  much  more  readily  attacked, 
perhaps  directly  as  follows: 

FeS2  +  KCy  =  FeS  +  KSCy. 

In  any  case,  under  ordinary  conditions  of  treatment,  pyrites 
rapidly  undergoes  oxidation,  forming  sulphates  and  basic  sul- 
phates of  iron,  which  act  readily  as  cyanicides.  Caldecott  * 
gives  the  following  as  the  main  stages  in  the  decomposition  of 
pyrite  or  marcasite: 

(1)  FeS2      Iron  pyrites. 

(2)  FeS  +  S     Ferrous  sulphide,  sulphur. 

(3)  FeSO4  +  H2SO4  ....  Ferrous  sulphate,  sulphuric  acid. 

(4)  Fe2(SO4)3 Ferric  sulphate. 

(5)  2Fe2O3  •  SO3     Insoluble  basic  ferric  sulphate. 

(6)  Fe2O3 Ferric  oxide. 

Ferrous  sulphide  is  injurious  owing  to  its  power  of  absorbing 

i  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  98. 


CHEMISTRY   OF  THE   DISSOLVING    PROCESS  111 

oxygen,  and  may  perhaps  actually  decompose  KAuCy2  so  as  to 
precipitate  gold  that  has  been  previously  dissolved.  Thio- 
cyanates  are  almost  invariably  present  in  cyanide  solutions  after 
use  in  extraction  of  ores.  As  sulphur  does  not  dissolve  directly 
in  cyanide,  they  may  be  due  to  the  action  on  pyrites,  as  stated 
above,  or  to  action  on  ferrous  sulphide: 

FeS  +  7KCy  +  H2O  +  O  =  KCyS  +  K4FeCy6  +  2KOH. 

All  the  iron  in  working  cyanide  solutions  probably  ultimately 
takes  the  form  of  soluble  alkali  ferrocyanides  (K4FeCye  or 
Na4FeCy6)  ,  since  ferrous  thiocyanate,  if  formed  at  all,  is  unstable 
and  would  react  with  KCy: 

Fe(CyS)2  +  6KCy  =  K4FeCy6  +  2KCyS. 

Ferrous  and  ferric  sulphates  act  directly  as  cyanicides,  ulti- 
mately giving  rise  to  Prussian  blue  and  similar  compounds,  or 
to  hydrocyanic  acid. 

In  the  case  of  ferrous  sulphate,  some  such  series  of  reactions 
as  the  following  may  be  supposed  to  take  place: 


FeS04  +  2KCy  =  FeCy2 
FeCy2  +  4KCy  =  K4FeCy6. 
2FeSO4  +  K4FeCy6  =  Fe2  •  FeCy6  +  2K2SO4. 
3Fe2FeCy6  +  3O  +  3H2O  =  Fe4(FeCy6)3  +  2Fe(OH)3. 

In  the  case  of  ferric  sulphate: 

Fe2(SO4)3  +  6KCy  =  2FeCy3  +  KzSO*. 
FeCy3  +  3H20  =  Fe(OH)3  +  3HCy. 

In  presence  of  sufficient  alkali  the  soluble  ferric  salts  are  pre- 
cipitated as  ferric  hydrate,  which  is  unacted  upon  by  cyanide;  l 
ferrous  salts  give  ferrous  hydrate,  which  readily  forms  ferro- 
cyanide,  as  above  described. 

The  basic  sulphates,  although  insoluble  in  water,  are  attacked 
by  cyanide,  giving  a  similar  series  of  reactions. 

Action  of  Copper  Compounds  on  Cyanide.  —  Copper  exists  in 
ores  most  frequently  as  sulphide,  often  combined  with  sulphides 
of  other  metals,  copper  pyrites  being  a  compound,  or  intimate 
mixture,  of  the  sulphides  of  iron  and  copper.  It  also  occurs  as 
native  copper,  and  in  oxidized  ores  as  carbonate,  oxide,  silicate, 
and  other  forms. 

i  According  to  Julian  and  Smart  ("  Cyaniding  Gold  and  Silver  Ores,"  2d 
edition,  p.  112),  "ferric  hydrate"  is  an  indefinite  compound,  Fe2O3.xH2O, 
which,  under  certain  conditions,  may  dissolve  in  cyanide,  forming  a  ferrocyanide. 


112  THE  CYANIDE   HANDBOOK 

Action  of  Cuprous  Sulphide.  —  The  natural  sulphides  of 
copper  are  much  less  readily  acted  on  by  cyanide  than  are  the 
carbonates,  or  than  artificially  prepared  sulphide,  but  they  grad- 
ually dissolve,  probably  with  formation,  finally,  of  cupric  thio- 
cyanate,  by  some  such  series  of  reactions  as  the  following: 

(a)  2Cu2S  +  4KCy  +  2H2O  +  O2  =  Cu2(CyS)2  +  Cu2Cy2  +  4KOH. 

The  insoluble  cuprous  thiocyanate  and  cyanide  readily  dis- 
solve in  excess  of  KCy: 

(6)  2Cu2(CyS)2  +  8KCy  +  H2O  +  O  =  2Cu(CyS)2  +  Cu2Cy2  •  6KCy  +  2KOH. 
(c)  Cu2Cy2  +  6KCy  -  Cu2Cy2  •  6KCy. 

Since  the  solutions  almost  invariably  contain  an  excess  of 
alkali  thiocyanate,  the  further  reaction  is  probably  as  follows: 

(d)  Cu2Cy2  -6KCy  +  4KCyS  +  H2O  +  O  =  2Cu(CyS)2  +  8KCy  +  2KOH. 

Action  of  Carbonate  of  Copper.  —  Carbonate  of  copper,  both 
native  and  artificial,  is  attacked  by  cyanide  with  extreme  rapidity, 
and  is  one  of  the  most  troublesome  cyanicides.  The  action,  when 
KCy  is  in  excess,  appears  to  be  as  follows: 

CuCO3  4-  2KCy  =  CuCy2  +  K2CO3. 
2CuCy2  +  4KCy  =  Cu2Cy2  •  4KCy  +  Cy2. 

When  sufficient  alkali  is  also  present: 

Cy2  +  2KOH  =  KCy  +  KCyO  +  H2O; 
so  that  the  entire  reaction  becomes: 
2CuCO3  +  7KCy  +  2KOH  =  Cu2Cy2  •  4KCy  +  KCyO  +  2K2CO3  +  H2O. 

Soluble  cupric  salts  (CuSO4,  etc.)  act  in  an  analogous  way, 
evolving  cyanogen  in  unprotected  solutions,  and  forming  double 
cyanides  probably  of  the  type  Cu2Cy2  •  nKCy. 

Removal  of  Copper  Before  or  During  Treatment.  —  Copper, 
when  present  in  the  form  of  carbonate,  oxide,  hydrate,  etc.,  may 
be  largely  removed  from  the  ore: 

(1)  By   preliminary   acid   treatment,   with   H2SO4   or   H2S03; 
any  acid  remaining  in  the  charge  after  this  operation  may  be 
neutralized  with  alkali  previous  to  cyanide  treatment. 

(2)  By  preliminary  treatment  with  ammonia,  which  dissolves 
many  copper  compounds  that  are  insoluble  in  water. 

(3)  In  the  course  of  cyanide  treatment,  by  the  use  of  a  mix- 
ture of  cyanide  with  ammonia  or  ammonium  salts.     Such  mixtures 


CHEMISTRY  OF   THE   DISSOLVING   PROCESS  113 

+         +       + 
are  largely  dissociated  in  dilute  solutions  into  the  ions  NH4,  K,  Na, 

and  CN,  Cl,  OH,  etc.;  they,  therefore,  act  as  powerful  solvents, 
and  appear  to  attack  gold  under  certain  conditions  in  preference 
to  copper.  The  copper  forms  "  cuprammonium  "  compounds  of 
the  type  xNH3  •  yCuCy2  •  zCu2Cy2,  which  are  only  slightly  soluble 
in  water,  forming  blue  solutions  from  which  green,  insolu- 
ble, needle-like  crystals  of  ammonium  dicuprosocupric  cyanide 
(4NH3  •  CuCy2  •  2Cu2Cy2)  are  deposited.  At  the  same  time  cyano- 
gen is  liberated,  which  at  the  moment  of  formation  readily  attacks 
gold  in  presence  of  excess  of  KCy: 

KCy  +  Cy  +  Au  =  KAuCy2. 

Gold  is  thus  dissolved  and  copper  precipitated  at  the  same  time. 
Copper  may  also  be  precipitated  from  solutions  by  the  addition 
of  acids;  thus: 


-nKCy  +  nH2SO4  =  Cu2Cy2  +  nHCy  +  nKHSO4; 
2Cu(SCy)2  +  H2SO4  =  Cu2(SCy)2  +  HSCy  +  HCy  +  2SO2 

forming  the  insoluble  cuprous  cyanide  and  thiocyanate. 

General  Action  of  Metallic  Sulphides.  —  Many  metallic  sul- 
phides are  more  or  less  soluble  in  alkalis,  with  formation  of  alka- 
line sulphides:  2KOH  +  R,,s  =  R*(OH)2  +  K,S. 

Since  the  cyanide  solutions  almost  invariably  contain  an  excess 
of  caustic  alkali,  this  reaction  takes  place  to  some  extent  in  the 
treatment  of  ores  containing  such  sulphides.  The  soluble  alka- 
line sulphide  locally  formed  may  sometimes  act  as  an  injurious 
factor  in  the  process,  owing  to  its  powerful  reducing  action,  which 
removes  the  oxygen  necessary  for  the  solution  of  the  gold.  It 
is,  however,  probably  *soon  converted  into  thiocyanate  by  the 
reaction  KzS  +  KCy  +  H2O  +  O  =  KCyS  +  2KOH. 

and  also  thrown  out  of  solution  by  the  reaction 
KaS  +  K2ZnCy4  =  ZnS  +  4KCy. 

It  is  partly  owing  to  this  latter  reaction  that  the  zinc,  dis- 
solved as  double  cyanide  in  the  precipitation  process,  is  removed 
from  the  solutions  before  it  has  accumulated  to  an  injurious 
extent. 

As  a  general  rule,  clean  unoxidized  minerals  have  only  a  slight 


114  THE  CYANIDE   HANDBOOK 

action  on  cyanide  solutions.  Christy's  experiments1  show  that 
nearly  all  such  minerals  are  electronegative  to  gold  in  cyanide 
solutions,  so  that  the  latter  would  dissolve  in  preference.  Never- 
theless, a  large  consumption  of  cyanide  is  sometimes  observed 
in  the  treatment  of  ores  containing,  for  example,  mispickel, 
realgar,  stibnite,  cinnabar,  galena,  blende,  fahl  ore,  sulphides  of 
nickel  and  cobalt,  etc.,  especially  when  the  sulphides  have  under- 
gone partial  oxidation. 

In  some  cases,  as  with  the  sulphides  of  arsenic,  antimony,  and 
tin,  it  is  possible  to  extract  the  cyanicide  by  a  preliminary  opera- 
tion, in  which  the  ore  is  treated  with  a  (preferably  hot)  solution 
of  an  alkali  or  alkaline  sulphide.  Zinc-blende  is  not  much  attacked 
by  cyanide,  but  calamine  is  a  rapid  cyanicide;  thus: 

ZnCO3  +  4KCy  =  K2ZnCy4  +  K2CO3. 

Action  of  Selenium  and  Tellurium.  —  Metallic  selenides, 
especially  when  finely  crushed,  are  dissolved  in  cyanide  without 
much  difficulty,  the  element  passing  into  solution  as  a  seleno- 
cyanide;  e.g.,  KSeCy. 

Tellurium  dissolves  with  more  difficulty,  perhaps  first  forming 
an  alkaline  telluride,  K2Te,  which  is  rapidly  converted  into  a 
tellurite,  K2TeO3. 

Ores  containing  considerable  quantities  of  refractory  minerals, 
especially  those  of  arsenic  and  tellurium,  are  perhaps  best  treated 
by  preliminary  roasting,  to  remove  or  oxidize  the  greater  part 
of  these  elements;  but  in  some  cases  they  have  been  successfully 
treated  by  very  fine  crushing,  followed  by  bromocyanide. 

When  an  ore  has  been  partially  oxidized,  either  by  natural 
processes  or  by  roasting,  it  is  very  necessary  to  extract  the  soluble 
matter  by  water-washing  previous  to  cyanide  treatment.  Such 
partially  oxidized  material  may  contain  large  amounts  of  soluble 
sulphates,  which  may  cause  a  very  much  larger  consumption  of 
cyanide  than  the  raw  unoxidized  ore.  Addition  of  alkalis,  with- 
out previous  water-washing,  is  not  always  a  satisfactory  remedy, 
as  metallic  hydrates,  such  as  Fe(OH)2,  may  be  precipitated, 
which  are  themselves  cyanicides. 

Oxides  of  manganese  sometimes  appear  to  form  very  easily 
decomposable  double  cyanides,  which  readily  deposit  the  brown 
hydrated  oxide. 

i  Trans.  A.  I.  M.  E.  (Sept.,  1899),  XXX,  33. 


CHEMISTRY  OF  THE  DISSOLVING   PROCESS  115 

Regeneration  of  Solutions.  —  Since  the  main  cause  of  cyanide 
consumption  is  the  formation  of  soluble  double  cyanides  or  com- 
plex cyanogen  compounds  of  the  base  metals,  and  since  solutions 
highly  charged  with  such  compounds  are  more  or  less  inefficient 
as  solvents  of  gold  and  silver,  it  has  been  suggested  that  the 
cyanogen  in  such  liquors  might  be  recovered  in  the  form  of 
simple  alkali  cyanides,  by  treatment  with  suitable  chemicals.  This 
has  been  carried  out  in  practice  in  some  cases,  but  generally 
speaking  the  cost  of  chemicals,  power,  labor,  etc.,  required  for 
such  treatment  outweighs  the  advantage  gained  by  it.  The 
following  methods  have  been  suggested  : 

(1)  The  solution  is  acidulated,  and  the  cyanogen  converted 
wholly  or  partially  into  hydrocyanic  acid,  in  some  cases  with 
precipitation  of  a  portion  as  insoluble  cyanides;  thus: 

K2ZnCy4  +  2H2SO4=  ZnCy2  +  2HCy  +  2KHSO4. 

ZnCy2  +  H2SO4  =  ZnSO4  +  2HCy. 
KAgCy2  +  H2SO4=  AgCy  +  HCy  +  KHSO4. 
4KCy  -Cu2Cy2  +  4H2SO4  =  Cu2Cy2  +  4HCy  +  4KHSO*. 


(2)  Ferric  salts  may  be  added,  to  precipitate  ferrocyanides 
as  Prussian  blue   (for  reactions  see  above).     After  drying,  the 
Prussian  blue  is  converted  into  an  alkali  cyanide  by  fusion  in  a 
closed  vessel  with  alkali  or  alkaline  carbonate. 

(3)  Alkaline    sulphides    decompose    the    double    cyanides    of 
silver,   mercury,  zinc,  cadmium  and  nickel,  precipitating  these 
metals  more  or  less  completely  as  sulphides  and  forming  a  soluble 
alkali  cyanide;  e.g.  : 

2KAgCy2  +  K.S  =  Ag2S  +  4KCy,  etc. 

The  reaction,  however,  is  never  complete,  as  the  sulphides 
formed  are  not  absolutely  insoluble  in  the  excess  of  cyanide. 
Moreover,  any  excess  of  sulphide  must  be  removed  and  the  solu- 
tion thoroughly  aerated  before  it  can  be  successfully  used  in  treat- 
ing fresh  charges  of  ore. 

Reprecipitation  of  Gold  and  Silver  during  Dissolving  Process.  — 
Under  certain  conditions,  a  premature  precipitation  of  gold  and 
silver  may  occur  in  the  leaching  tanks  or  other  parts  of  the  dissolv- 
ing plant,  and  may  lead  to  losses.  It  is  well  known  that  charcoal 
is  a  precipitant  of  gold  from  cyanide  solutions;  an  admixture  of 
carbonaceous  matter  may  therefore  cause  local  precipitation  of 
values  previously  dissolved.  This  was  a  frequent  cause  of  trouble 


116  THE  CYANIDE   HANDBOOK 

with  the  black  cyanide  formerly  in  use  (containing  carbon  and 
carbides  of  iron).  When  this  cyanide  was  dissolved,  it  left  a 
layer  of  black  sediment,  which  sometimes  contained  considerable 
values  after  being  some  time  in  contact  with  the  auriferous  solu- 
tions. Decaying  organic  matter,  such  as  grass  roots,  etc.,  may 
likewise  cause  losses  in  this  way. 

Local  acidity  of  the  ore  may  cause  precipitation  of  insoluble 
aurous  cyanide: 

KAuCy2  +  H2SO4  =  AuCy  +  HCy  +  KHSO4. 

Under  some  circumstances  gold  and  silver  may  be  thrown 
down  as  insoluble  salts,  by  the  action  of  soluble  base  metal  salts; 
thus:  2KAgCy2  +  ZnSO4  =  K2SO4  +  ZnAg2Cy4. 

The  action  of  alkaline  sulphides  on  silver  double  cyanide  has 
already  been  noted;  gold  is  not  precipitated  by  these  reagents. 
Some  metallic  sulphides,  such  as  Cu2S,  seem  to  have  the  power 
of  throwing  down  gold  from  a  cyanide  solution. 


SECTION   V 

CHEMISTRY   OF   PRECIPITATION   AND    SMELTING 
PROCESSES 

IT  has  already  been  pointed  out  that  gold  and  silver  are  electro- 
negative to  zinc  in  cyanide  solutions;  hence  we  should  expect 
that  zinc  would  act  as  a  precipitant  of  the  precious  metals.  This 
effect,  however,  is  obviously  complicated  by  various  secondary  re- 
actions. The  following  points  are  always  noticed  in  this  connec- 
tion: 

(a)  Precipitation  only  takes  place  in  presence  of  sufficient 
free  cyanide. 

(6)  It  is  always  accompanied  by  increase  in  the  alkalinity 
of  the  solution. 

(c)  It  is  always  accompanied  by  evolution  of  hydrogen. 

The  entire  effect,  as  regards  precipitation  of  gold,  is  probably 
expressed  by  the  equation: 

KAuCy2  +  2KCy  +  Zn  +  H2O  =  K2ZnCy4  +  Au  +  H  +  KOH; 

but  the  solution  of  zinc  goes  on  to  a  large  extent  quite  inde- 
pendently of  the  precipitation  of  gold,  and  bears  no  necessary 
proportion  to  it.  The  probable  reaction  is 

Zn  +  4KCy  +  2H2O  =  K2ZnCy4  +  2KOH  +  H2, 

though  some  writers  have  supposed  that  an  alkaline  zincate, 
such  as  Zn(OK)2,  may  be  formed. 

It  would  appear  that  the  electric  couples  Zn:  Pb  and  Zn:  Au, 
etc.,  give  rise  to  local  currents  which  electrolyze  water,  the  oxygen 
at  the  moment  of  formation  attacking  zinc  to  form  hydroxide: 

Zn  +  O  +  H20  =  Zn(OH)2. 

Under  the  usual  working  conditions  this  redissolves  in  the  excess 
of  cyanide;  thus: 

Zn(OH)2  +  4KCy  =  K2ZnCy4  +  2KOH; 

but  an  insufficiency  of  free  cyanide  may  lead  to  its  deposition  in 
the  form  of  a  white  precipitate  on  the  surface  of  the  shavings. 

117 


118  THE  CYANIDE  HANDBOOK 

As  before  pointed  out,  the  double  cyanides  of  zinc  and  alkali 
metals  may  be  assumed  partially  to  dissociate  in  dilute  solutions, 
so  that  we  have  KCy,  NaCy,  and  ZnCy2  actually  in  solution,  and 
these  are,  perhaps,  still  further  split  up.  In  the  absence  of  suffi- 
cient free  alkali  or  alkaline  cyanide,  this  ZnCy2  may  also  be  de- 
posited. 

Sharwood  1  has  investigated  the  conditions  under  which  zinc 
oxide  dissolves  in  cyanide,  and  zinc  cyanide  in  alkaline  hydrox- 
ides. He  finds  that  ZnO  is  soluble  in  .65  per  cent.  KCy  with 
formation  of  a  double  cyanide,  and  of  a  compound  of  zincate  with 
excess  of  alkaline  hydrate: 

20KCy  +  6ZnO  +  4H2O  =  5K2ZnCy4  +  K2ZnO2  -8KOH; 
the  latter  being  the  result  of  a  secondary  reaction;  thus: 

4KCy  +  ZnO  +  H2O  =  K2ZnCyi  +  2KOH; 
10KOH  +  ZnO  =  K2ZnO2  •  8KOH  +  H2O. 

The  action  of  KOH  on  ZnCy2  is  as  follows: 

(a)  When  the  ZnCy2  is  in  less  proportion  than  ZnCy2:  2KOH 
it  dissolves  completely  and  permanently: 

4KOH  +  2ZnCy2  =  K2ZnCy4  +  K2ZnO2  +  2H2O. 
On  heating,  the  zincate  decomposes: 

K2ZnO2  +  2H2O  =  Zn(OH)2  +  2KOH. 

(b)  When  ZnCy2  is  in  the  proportion  ZnCy2:KOH,  it  is  tem- 
porarily dissolved,  but  soon  begins  to  precipitate  Zn(OH)2,   as 
follows:  2ZnCy2  +  2KOH  =  K2ZnCy4  +  Zn(OH)2. 

(c)  With  larger  proportions  of  ZnCy2  any  excess  remains  un- 
affected by  KOH. 

NaOH  acts  in  a  similar  way. 

It  seems  probable  that  any  excess  of  KCy  would  convert  the 
zincate  into  the  double  cyanide,  but  as  increasing  the  alkalinity 
undoubtedly  increases  the  solvent  efficiency  of  the  solution,  it 
may  be  that  we  have  here  a  reversible  reaction: 

K2ZnCy4  +  4KOH  ;=!  Zn(OK)2  +  4KCy  +  2H2O. 

Various  investigators  have  made  more  or  less  complete  analyses 
of  the  white  precipitate  above  referred  to;  somewhat  conflicting 
results  have  been  obtained,  and  the  substance  no  doubt  varies 
according  to  the  conditions  of  formation.  Experience  has  shown 

i  "Bull.  Univ.  Cal.,"  April  27,  1904. 


CHEMISTRY  OF   PRECIPITATION  119 

that  the  formation  of  the  precipitate  is  greatly  promoted  by 
exposure  of  the  zinc  shavings  to  the  air.  It  occurs  chiefly  as  a 
flocculent,  whitish  deposit  in  the  upper  compartments  of  the 
boxes,  and  often  interferes  seriously  with  effective  precipitation 
of  the  gold  and  silver.  The  general  conclusion  is  that  it  consists 
principally  of  zinc  hydrate,  with  smaller  quantities  of  cyanide 
and  ferrocyanide  of  zinc,  with  small  amounts  -of  the  sulphates 
and  carbonates  of  calcium,  lead,  etc.;  also  alumina,  silica,  and 
other  ingredients  of  less  importance.  The  following  analyses 
give  some  idea  of  its  composition: 

(1)  By  A.   Whitby1    (the  metals   being  calculated   as    their 
equivalent  oxides) : 

ZnO    54.00  per  cent. 

SiO2  and  insoluble    2.10 

Fe2O3  +  A12O3 75 

PbO 73 

CaO    .  .50 

CN    2.50 

K2O    70 

Loss  on  ignition     36.80 

(2)  By  Bay  and  Prister2: 

Zinc  hydrate,  Zn(OH)2     54.79  per  cent. 

Zinc  cyanide,  ZnCy2    22.73 

Zinc-potassium  ferrocyanide,  K2Zn3(FeCy6)2 10.45 

Silica,  SiO2    1.03 

Ferric  oxide,  Fe2O3    1.00 

Cupric  oxide,  CuO     40 

The  zinc  hydrate  and  cyanide  are  readily  soluble  in  excess 
of  KCy  or  of  caustic  alkali  (also  in  dilute  acids),  but  the  ferro- 
cyanide is  not  easily  soluble,  and  if  once  formed  generally  re- 
mains in  the  boxes  until  the  clean-up. 

There  are  grounds  for  supposing  that  gold  and  silver  are  pre- 
cipitated on  zinc,  either  in  the  metallic  condition  or  as  an  alloy, 
according  to  the  concentration  of  the  liquors  undergoing  pre- 
cipitation in  metal  and  cyanide.  Argall  states  that  when  the 
solutions  pass  1.5  ounces  gold  per  ton,  the  gold  on  the  shavings 
assumes  a  yellow  color,  and  passing  2  ounces  and  upward  is 
usually  golden  yellow  in  the  first  compartment,  shading  off  in 

1  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  V,  55. 
*IUd.,  V,  77. 


120  THE  CYANIDE  HANDBOOK 

the  following  compartments  to  the  usual  black-colored  deposit 
obtained  from  poor  solutions. 

The  alloys  so  formed  are  more  energetically  attacked  than 
pure  zinc  by  the  cyanide  solutions,  and  hence  act  more  efficiently 
as  precipitants.  Silver  also  presents  a  totally  different  appearance, 
according  to  the  conditions  of  precipitation. 

Action  of  Copper  in  Precipitation  with  Zinc.  —  Solutions  con- 
taining copper  deposit  this  metal  in  the  upper  compartments 
of  the  zinc-box;  the  copper  forms  a  closely-adherent  metallic 
film,  which  coats  the  zinc  shavings  in  such  a  way  that  all  further 
action  ceases  and  the  precipitation  of  gold  and  silver  is  prevented. 
In  strong  solutions,  copper  is  precipitated  in  preference  to  gold 
and  silver.  When  copper  has  accumulated  to  a  certain  extent 
in  the  solution,  it  becomes  practically  impossible  to  use  the  liquor 
either  for  extraction  of  gold  and  silver  or  for  precipitation,  and 
the  copper  must  be  removed  by  some  means  or  the  liquor  run  to 
waste. 

The  zinc-lead  couple  has  been  sometimes  used  with  advantage 
for  cupriferous  solutions;  certain  compartments  filled  with  zinc 
shavings  previously  dipped  in  lead  acetate  are  found  to  collect 
most  of  the  copper.  Barker,1  however,  says  that  although  "  with 
a  good  spongy  coating  of  lead  on  the  zinc  the  precipitation  of 
the  copper  is  at  first  good,  the  copper  coming  down  in  a  loose 
spongy  form,"  the  action  is  not  continuous.  He  therefore  sug- 
gests precipitating  as  cuprous  cyanide  by  the  addition  of  sulphuric 
acid.  When  the  copper  exists  in  the  solutions  as  a  double  cy- 
anide (e.g.,  Cu2Cy2  •  4KCy,  or  Cu2Cy2  •  6KCy),  the  precipitation 
of  copper  is  accompanied  by  regeneration  of  cyanide,  as  shown 
by  the  following  reactions  : 

Cu2Cy2  •  4KCy  +  Zn  =  Cu2  +  K2ZnCy4  +  2KCy. 
6KCy  +  Zn  =  Cu2  +  K2ZnCy4  +  4KCy. 


Small  quantities  of  mercury  are  almost  invariably  present  in 
the  solution  before  precipitation.     Mercury  is  carried  off  mechani- 
cally with  the  tailings  from  the  battery  and  gradually  dissolves 
to  furm  K2HgCy4.     In  some  cases  it  may  also  be  partly  derived 
from  mercury  minerals  contained  in  the  ore  itself.     The  com- 
pound is  directly  decomposed  by  zinc,  as  follows: 
K2HgCy4  +  Zn  =  K2ZnCy4  +  Hg. 
*  Trans.  I.  M.  M.,  XII,  399. 


CHEMISTRY   OF   PRECIPITATION  121 

As  already  pointed  out,  the  double  cyanides  of  mercury  are 
gold  solvents,  and  also  act  by  decomposing  soluble  sulphides, 
so  that  the  presence  of  this  metal  in  small  quantities  is  a  distinct 
advantage. 

The  precipitate  formed  in  the  zinc-boxes  occasionally  contains 
other  elements;  such  as  arsenic,  antimony,  selenium,  tellurium, 
etc.,  derived  from  the  material  treated.  The  removal  of  these 
in  the'  subsequent  treatment  may  involve  special  operations, 
as  noted  below.  Whenever  the  zinc  shavings  have  been  treated 
with  lead  acetate,  the  precipitate  will  contain  a  certain  amount 
of  metallic  lead. 

Electrolytic  Precipitation.  —  Many  methods  have  been  tried 
or  suggested  for  precipitating  gold  and  silver  electrolytically 
from  cyanide  solutions.  The  best  known  is  that  of  Siemens  and 
Halske,  which,  in  the  form  originally  adopted  in  South  Africa, 
used  anodes  of  iron  and  cathodes  of  lead.  The  cathodes  were 
not  attacked  under  ordinary  circumstances,  but  an  adherent 
deposit  of  gold  was  formed  upon  them.  Under  the  influence  of 
the  electric  current  the  aurocyanide  is  ionized  into 

+      +.    + 

K(or  Na),  Au  and  Cy  Cy. 

The  K,  of  course,  goes  to  form  KOH  and  liberates  H  at  the  cathode. 
The  Cy  attacks  the  iron  anode,  ultimately  forming  ferrocyanide 
and  a  certain  amount  of  Prussian  blue,  ferric  hydrate,  and  per- 
haps other  by-products. 

Afterward,  the  cathodes  and  anodes  in  use  were  both  of  lead, 
but  the  lead  anodes  were  found  to  become  brittle  after  a  time 
and  were  coated  superficially  with  a  white  deposit,  probably 
oxycyanide  of  lead. 

Tinned  iron  cathodes  with  lead  anodes  were  also  used  at  one 
time;  the  current  density  was  so  regulated  that  the  gold  was 
precipitated,  not  in  an  adherent  form,  but  as  a  loose  powder 
which  continually  fell  off  the  cathodes  and  settled  at  the  bottom 
of  the  box,  whence  it  could  be  easily  collected  in  cleaning  up. 
In  the  latest  form  of  the  process,  adopted  at  the  San  Sebastian 
Mine,  Salvador,  Central  America,1  the '  cathodes  are  rolled  lead 
plates,  and  the  anodes  are  similar  lead  plates  which  have  been 
previously  coated  with  a  layer  of  peroxide  of  lead  by  immersing 

i  C.  P.  Richmond,  "  Eng.  and  Min.  Journ., "  LXXX,  512. 


122  THE  CYANIDE  HANDBOOK 

in  a  solution  of  permanganate.  The  difficulty  with  regard  to 
copper  is  got  over  in  the  plant  referred  to  by  using  electric  pre- 
cipitation for  recovering  part  of  the  copper  and  gold  and  then 
passing  the  solution,  comparatively  free  from  copper,  through 
ordinary  zinc-boxes  to  recover  the  residual  gold. 

Other  electrolytic  methods,  using  amalgamated  zinc  or  copper 
as  electrodes,  have  also  been  tried,  but  with  little  practical  suc- 
cess. Aluminium  has  been  suggested  as  a  material  for  the  elec- 
trodes, but  although  effective  as  a  precipitant,  it  causes  much 
difficulty  by  forming  infusible  compounds  in  the  subsequent  smelt- 
ing operations. 

Other  Precipitation  Processes.  —  Aluminium  in  the  form  of 
shavings  has  also  been  suggested,  and  occasionally  tried  on  a 
working  scale,  as  a  substitute  for  zinc,  without  the  aid  of  elec- 
tricity. It  is  even  more  electro-positive  than  zinc,  but  a  deposit 
of  alumina  is  formed  on  the  shavings  and  causes  much  trouble 
in  the  treatment  of  the  precipitate. 

Sodium  amalgam  has  been  used,  either  directly  or  in  conjunc- 
tion with  an  electric  current.  Theoretically,  the  action  is  very 
Simple:  KAuCy2  +  Na  =  Au  +  KCy  +  NaCy; 

but  in  practice  it  is  found  that  the  large  surface  required  precludes 
the  economic  application  of  the  process. 

In  the  Gilmour- Young  process  the  ore  is  subjected  to  com- 
bined pan-amalgamation,  and  cyanide  treatment.  After  grinding 
in  pans  with  mercury  and  cyanide  solution,  copper  and  zinc 
amalgam  are  added,  which  precipitate  the  gold  from  the  solution. 
The  gold  amalgamates  and  can  be  recovered  by  retorting,  like 
ordinary  battery  gold. 

Other  methods  involving  the  use  of  amalgams  are  the  Pelatan- 
Clerici  and  Riecken  processes. 

Charcoal  was  at  one  time  extensively  used  as  a  precipitant 
in  Victoria,  Australia,  The  chemical  action  by  which  it  pre- 
cipitates gold  is  somewhat  obscure,  but  is  supposed  to  depend 
on  the  occlusion  of  certain  gases  in  the  pores  of  the  charcoal 
which  act  on  and  decompose  the  aurocyanide  in  the  percolating 
solutions.  An  enormous  volume  is  required  for  effective  pre- 
cipitation. 

Other  suggested  methods  of  precipitation  involve  the  use  of 
chemicals  which  destroy,  or  at  least  enter  into  combination  with, 


CHEMISTRY  OF   PRECIPITATION  123 

the  whole  of  the  cyanogen  present  in  the  solution  as  simple 
cyanides.  These  cannot  be  considered  to  have  passed  the  experi- 
mental stage.  S.  B.  Christy  and  P.  de  Wilde  have  observed 
independently  that  soluble  cuprous  salts,  added  to  a  cyanide 
solution,  produce  a  precipitate  of  white  cuprous  cyanide,  which 
carries  down  with  it  practically  the  whole  of  the  gold  and  silver; 
but  this  reaction  only  takes  place  in  acid  solutions,  and  would 
involve  the  neutralization  of  enormous  quantities  of  alkali. 

Soluble  silver  salts  give  a  precipitate  of  silver  cyanide  when 
added  in  sufficient  excess,  or  to  an  acidulated  solution;  practically 
the  whole  of  the  gold  is  carried  down;  but  this,  of  course,  is  only 
a  laboratory  method. 

Final  Operations.  —  In  the  clean-up,  apart  from  mechanical 
operations,  we  have  to  consider  three  processes  involving  chemical 
reactions:  (1)  Acid  treatment;  (2)  roasting;  (3)  smelting. 

Acid  Treatment.  —  The  precipitate  as  obtained  from  the 
zinc-boxes  invariably  contains  a  considerable  amount  of  metallic 
zinc  in  fine  shreds  or  particles  which  pass  through  the  sieves. 
This  can  be  largely  removed  by  treatment  with  sulphuric  or 
hydrochloric  acid,  the  zinc  dissolving  as  sulphate  or  chloride. 
In  some  cases  sodium  bisulphate  (NaHSO4),  which  is  a  by- 
product in  the  manufacture  of  nitric  acid  and  may  be  obtained 
at  a  low  cost,  has  been  used  with  advantage  as  a  substitute  for 
H2SO4,  the  reaction  being: 

2NaHSO4  +  Zn  =  NaaSO*  +  ZnSO4  +  H2. 


In  the  case  of  precipitates  containing  As,  Sb,  Se,  and  Te, 
these  elements  are  partially  evolved  as  the  hydrides  AsH3,  SbH3, 
SeH2,  and  TeH2,  on  treatment  with  sulphuric  or  hydrochloric 
acids;  these  gases  are  very  offensive  and  poisonous,  and  in  the 
case  of  AsH3  have  several  times  been  the  cause  of  fatal  accidents. 
In  all  cases,  considerable  amounts  of  HCy  are  evolved  from  the 
decomposition  of  the  cyanogen  compounds  contained  in  the 
precipitate.  Preliminary  treatment  with  nitric  acid  has  there- 
fore been  recommended;  this  converts  cyanides  into  cyanates, 
arsenic  into  arsenic  acid,  selenium  and  tellurium  into  selenious 
and  tellurous  acids.  These  compounds,  being  non-volatile, 
give  rise  to  no  noxious  fumes,  and  are  carried  off  in  solution  after 
the  treatment.  There  may,  however,  be  losses  of  silver  and 
possibly  also  of  gold. 


124  THE   CYANIDE   HANDBOOK 

When  zinc  dust  is  used  as  a  precipitant,  some  difficulty  has 
been  experienced  (as  at  Mercur,  Utah) ,  in  treating  the  precipitate 
obtained,  when  sulphuric  acid  alone  has  been  used.  It  packs 
very  hard,  and  the  particles  of  zinc  appear  in  some  cases  to  become 
coated  with  a  layer  of  gold  which  protects  them  from  further 
action.  A  mixture  of  sulphuric  and  nitric  acids  was  found  to  be 
a  more  efficient  solvent. 

Objection  has  been  raised  to  the  use  of  hydrochloric  acid  on 
the  ground  that  it  may  liberate  chlorine  under  certain  circum- 
stances, thus  involving  loss  of  gold.  It  is,  moreover,  considerably 
more  costly  than  sulphuric  acid  in  most  places. 

Whatever  treatment  be  adopted,  the  solution  of  the  zinc  is 
always  incomplete.  It  is  possible  that  among  the  various  alloys 
which  may  be  formed  there  are  some  that  are  not  readily  attacked 
by  acids;  also  in  some  cases  protective  coatings  of  PbSO4  or  CaS04 
may  be  formed. 

Roasting.  —  The  main  object  of  this  operation  is  to  oxidize 
the  metallic  zinc  to  ZnO,  which  in  the  subsequent  smelting  passes 
into  the  slag  as  silicate  of  zinc,  whereas  metallic  zinc  would  pass 
into  the  bullion.  Any  other  oxidizable  metals  are  also  oxidized, 
and  cyanogen  compounds  either  completely  destroyed  or  con- 
verted into  cyanates.  Arsenic,  antimony,  selenium  and  tellu- 
rium are  partially  volatilized  as  oxides,  but  it  is  not  possible 
to  completely  remove  them  in  this  way,  and  the  fumes  may 
mechanically  carry  off  considerable  amounts  of  gold  and  silver. 

A  partial  oxidation  of  the  zinc  is  sometimes  brought  about 
in  a  preliminary  operation  by  mixing  the  precipitate  with  niter 
and  drying  in  shallow  pans  at  a  low  heat. 

The  roasting  may  be  done  in  pans  over  an  open  fire,  in  a  muffle, 
or  in  a  reverberatory  furnace. 

Smelting.  —  This  operation  aims  at  producing  bullion  as  free 
as  possible  from  base  metals  and  other  impurities.  As  the  pre- 
cipitate, after  acid  treatment  and  roasting,  still  contains  silica, 
insoluble  calcium  salts,  and  considerable  amounts  of  zinc,  lead, 
and  other  base  metals,  the  flux  required  must  be  varied  according 
to  its  composition.  The  chief  ingredients  used  as  fluxes  are: 

1.  Borax,  to  produce  fusible  borates  of  iron,  aluminium,  and 
other  metals. 

2.  Silica  (if  not  already  present  in  sufficient  quantity),   to 
form  silicate  of  zinc. 


CHEMISTRY  OF   PRECIPITATION 


125 


3.  Carbonate  of  soda,  to  form  a  more  fusible  silicate,  to  flux 
any  excess  of  silica,  and  in  some  cases  to  form  fusible  double 
sulphides. 

4.  Fluorspar,  to  flux  infusible  calcium  sulphate,  and  generally 
to  increase  the  fluidity  of  the  slag. 

5.  Oxidizing  agents  (niter,  MnO2,  etc.),  to  oxidize  any  base- 
metal  sulphides,  selenides,  tellurides,  carbonaceous  matter,  etc. 

Metallic  iron  is  also  sometimes  added,  to  reduce  base-metal 
sulphides,  etc.  In  some  cases  a  matte  is  formed,  which  requires 
special  treatment  for  reduction  to  bullion.  The  slags  are  some- 
times remelted  with  addition  of  fresh  flux,  to  which  litharge  is 
added,  whereby  a  large  part  of  the  value  is  collected  as  lead 
bullion,  and  the  resulting  low-grade  slag  may  safely  be  rejected. 

Lead  Smelting  of  Zinc  Precipitate.  —  In  the  Tavener  process 
the  zinc  precipitate  is  smelted  direct  with  litharge,  siliceous 
material,  and  a  reducing  agent,  the  object  being  to  form  a  lead 
alloy  of  the  gold  and  silver  and  to  flux  off  the  zinc,  etc.,  as  fusible 
silicates  in  one  operation.  The  litharge  is  reduced  as  follows: 

2PbO  +  C  =  CO2  +  2Pb. 

The  lead  bullion  is  then  cupeled,  and  the  litharge  formed  in  this 
operation  recovered  for  use  in  future  smelting  charges. 

Bullion  is  often  further  refined  by  remelting  with  fresh  flux, 
and  in  some  cases  by  oxidizing  by  means  of  a  blast  of  air  directed 
on  the  surface  of  the  molten  metal.  Attempts  have  also  been 
made  to  refine  by  injecting  air  or  oxygen  into  the  crucible  con- 
taining the  molten  bullion. 

According  to  T.  K.  Rose,1  the  following  is  the  order  in  which 
metals  are  oxidized  under  such  conditions;  the  table  given  also 


Metal 

Oxide 

Heat  of  Combination  with  O 

Zinc  

ZnO 

827 

Iron                

Fe2O3 

637 

Lead 

PbO 

503 

Nickel  

Ni2O3 

401 

Copper             

Cu2O 

372 

Platinum 

PtO 

179 

Silver  

Ag2O 

59 

Gold 

AuO 

—    44 

Trans.  I.  M.  M.,   XIV,   p.  384. 


126  THE  CYANIDE  HANDBOOK 

shows  the  heat  of  combination,  the  number  given  being  the  num- 
ber of  grams  of  water  which  would  be  raised  from  0°  to  100°  C., 
by  the  combination  of  16  grams  of  oxygen  with  the  metal  in 
question. 


SECTION  VI 

MANUFACTURE   OF  CYANIDE 

THE  various  processes  for  the  manufacture  of  cyanide  may  be 
classified  according  to  the  source  from  which  the  nitrogen  is 
derived.  The  principal  methods  in  use  are: 

(a)  Those  in  which  refuse  animal  matter  is  used  as  the 
nitrogenous  raw  material,  ferrocyanide  being  generally  produced 
as  an  intermediate  product. 

(6)  Those  in  which  atmospheric  nitrogen  is  employed  to  form 
cyanide  compounds,  directly  or  indirectly. 

(c)  Those  in  which  ammonia  or  ammonium  compounds 
form  the  nitrogenous  raw  material,  including  methods  which 
utilize  residues  from  gas-works. 

(a)  PRODUCTION  OF  CYANIDES  FROM  REFUSE  ANIMAL  MATTER 

Until  about  the  year  1890,  this  was  the  method  almost  uni- 
versally used.  The  raw  materials  required  are:  (1)  Nitrogenous 
animal  matter,  such  as  horns,  hoofs,  dried  blood,  wool,  woollen 
rags,  hair,  feathers,  leather-clippings,  etc.  (2)  An  alkaline  car- 
bonate, such  as  pearl-ash,  soda-ash,  etc.  (3)  Iron  filings  or 
borings. 

The  alkali  and  the  iron  are  first  fused  together  at  a  moderate 
heat  in  an  iron  pan,  or  other  suitable  vessel,  contained  in  a 
reverberatory  furnace.  The  well-dried  animal  matter  is  then 
introduced  in  small  quantities  at  a  time  and  stirred  in.  The  heat 
is  then  raised  and  the  furnace  closed  so  as  to  maintain  a  reducing 
atmosphere.  The  hard  black  mass  which  forms  is  then  taken 
out  and  lixiviated  with  nearly  boiling  water.  The  crude  ferro- 
cyanide containing  sulphides,  sulphates,  carbonates  and  thio- 
cyanates,  is  crystallized  out  and  purified  by  recrystallization. 
The  ferrocyanide  was  formerly  converted  into  cyanide  by  first 
dehydrating  and  then  fusing,  either  alone  or  with  alkaline 
carbonate : 

K4Fe(CN)6 + K2CO3  =  5KCN + KCNO + Fc + COa 
127 


128  THE  CYANIDE  HANDBOOK 

The  cyanide  so  formed  is  always  contaminated  with  cyanates  and 
carbonates,  and  generally  with  small  amounts  of  other  salts 
(sulphides,  chlorides,  thiocyanates,  etc.). 

The  procedure  frequently  adopted  at  present  is  to  fuse  with 
metallic  sodium: 

K4FeCy6  +  2Na  =  4KCy  +  2NaCy  +  Fe; 

thus  yielding  a  mixture  of  potassium  and  sodium  cyanides  free 
from  cyanates,  etc.  The  presence  of  sulphides  and  thiocyanates 
in  the  product  is  due  chiefly  to  the  sulphur  contained  in  the 
organic  matter.  These  compounds  are  partially  decomposed 
and  removed  by  metallic  iron  during  the  fusion.  When  the  cy- 
anide is  made  by  direct  fusion  of  ferrocyanide,  the  product  con- 
tains carbide  of  iron,  some  nitrogen  being  given  off  in  the  process. 
Most  of  the  volatile  organic  nitrogen  is  lost  in  the  form  of 
ammonia  or  nitrogen  gas  during  the  fusion  for  ferrocyanides,  in 
the  first  stage  of  the  process. 

(6)  PRODUCTION  OF  CYANIDES  FROM  ATMOSPHERIC  NITROGEN 

It  was  observed  by  Scheele  that  when  nitrogen  is  passed  over 
a  mixture  of  K2CO3  and  charcoal  heated  to  redness,  a  cyanide  of 
potassium  is  formed.  Many  attempts  were  made  throughout 
the  nineteenth  century  to  utilize  this  reaction  for  industrial 
purposes.  One  of  the  earliest  was  that  of  Possoz  and  Boissiere, 
who  used  a  mixture  of  charcoal  with  30  per  cent,  of  potassium 
carbonate.  This  was  kept  at  a  red  heat  in  fire-clay  cylinders, 
through  which  a  mixture  of  N  and  CO,  produced  by  passing  air 
over  red-hot  alkalized  carbon,  was  allowed  to  pass  for  about  10 
hours.  The  product  was  then  lixiviated  with  water  in  presence 
of  ferrous  carbonate  (spathic  iron  ore)  to  give  a  ferrocyanide. 

It  was  also  observed  at  an  early  date  (by  Clark,  in  1837), 
that  cyanides  are  formed  as  an  efflorescence  in  blast-furnaces, 
and  that  the  gases  of  these  furnaces  contain  cyanogen.  Bunsen 
proposed  a  special  blast-furnace  for  the  production  of  cyanide, 
in  which  coke  and  potash  in  alternate  layers  were  to  be  heated 
by  a  strong  blast,  the  fused  cyanide  running  off  at  the  bottom 
of  the  furnace.  It  was  found,  however,  that  a  very  high  tempera- 
ture was  necessary,  as  the  potassium  compound  must  be  reduced 
to  metallic  potassium  before  combination  with  atmospheric  nitro- 
gen takes  place. 


MANUFACTURE    OF    CYANIDE  129 

Better  results  were  obtained  by  substituting  barium  carbonate 
for  K2CO3,  as  in  the  process  of  Margueritte  and  DeSourdeval 
(1861).  Air  (deoxygenated  by  hot  carbon)  was  passed  over  a 
previously  ignited  mixture  of  BaCO3,  iron-filings,  coal  tar,  and 
sawdust,  whereby  barium  cyanide  is  produced.  This  is  converted 
into  sodium  cyanide  by  fusion  with  sodium  carbonate.  The 
BaC03  is  first  reduced  to  barium  carbide  (BaC2) : 

BaCO3  +  4C  =  BaC2  +  SCO. 

This  then  combines  with  nitrogen  to  form  Ba(CN)2.  It  has  been 
found,  however,  that  only  about  30  per  cent,  of  the  barium  is 
converted  to  cyanide,  the  remainder  forming  barium  cyanamide 
by  a  secondary  reaction: 

Ba(CN)2  =  C  +  BaCN2. 

When  calcium  is  substituted  for  barium  in  this  process,  prac- 
tically the  whole  is  converted  into  calcium  cyanamide: 

CaC2  +  N2  =  C  +  CaCN2. 

Calcium  cyanamide  is  also  formed  in  the  electric  resistance 
furnace  by  passing  nitrogen  over  a  mixture  of  lime  and  charcoal: 

CaO  +  2C  +  N2  =  CaCN2  +  CO. 

By  heating  the  product  at  a  high  temperature  with  a  further 
quantity  of  carbon,  with  the  addition  of  salt  to  prevent  frothing 
and  facilitate  the  reaction,  the  cyanamide  is  converted  into 
cyanide  as  follows:  CaCN2  +  c  =  Ca(CN)2. 

The  crude  mixture  so  formed  has  been  used  as  a  substitute  for 
potassium  cyanide  under  the  name  of  "Cyankalium  surrogat," 
and  is  equivalent  in  cyanogen  contents  to  about  30  per  cent. 
KCN.  [See  Erlwein  and  Frank,  U.  S.  patent,  708,333.] 

An  improved  method  more  recently  introduced  is  to  convert 
the  calcium  cyanamide  into  sodium  cyanide  by  the  following 
series  of  reactions: 

(1)  By  leaching  with  water,  a  crystallizable,  easily  purified 
salt  is  obtained,  known  as  dicy an-diamide : 

2CaCN2  +  4H20  =  (CN  •  NH2)2  +  2Ca(OH)2. 

(2)  This,   when   fused   with   sodium   carbonate   and   carbon, 
is  largely  converted  into  sodium  cyanide: 

(CN  -NH2)2  +  Na2C03  +  2C  =  2NaCN  +NH3  +  N  +  H  +  3CO 


!3Q  THE  CYANIDE  HANDBOOK 

A  portion  of  the  dicyan-diamide  sublimes  and  polymerizes ;  this  is  recovered 
and  re-treated  with  Na2CO3  in  a  subsequent  operation.  The  cyanamide  and  di- 
cyan-diamide are  also  utilized  as  sources  of  products  valuable  as  manures,  as 
they  can  be  readily  converted  into  ammonia,  ammonium  carbonate,  urea,  etc. 

Cyanides  may  also  be  formed  by  the  action  of  metallic  sodium 
and  carbon  on  atmospheric  nitrogen  (Castner) ;  but  it  is  prefer- 
able to  use  ammonia  as  the  source  of  nitrogen  in  this  reaction 
(see  below). 

(c)  PRODUCTION    OF   CYANIDES  FROM  AMMONIA    OR    AMMONIUM 

COMPOUNDS 

When  ammonia  is  passed  over  mixtures  of  heated  alkali  and 
carbon,  only  small  quantities  are  converted  into  cyanide;  better 
results  are  obtained  by  passing  CO  and  NH3  through  a  molten 
mixture  of  KOH  and  carbon,  but  even  by  this  means  much  of 
the  ammonia  is  dissociated  into  N  and  H,  owing  to  the  great 
heat  which  is  necessary.  It  is  supposed  that  potassamide  is  an 
intermediate  product: 

KOH  +  NH3  !=;  K  -  NH2  +  H2O  (reversible). 
K  •  NH2  +  CO  =  KCN  +  H2O. 

In  Castner's  process  (Brit,  patents,  12,218,  12,219,  of  1894), 
molten  sodium  is  allowed  to  flow  through  a  mass  of  heated  coke 
while  ammonia  gas  is  passed  upward,  the  reaction  being 

2NH3  +  2C  +  2Na  =  2NaCN  +  3H2. 

The  reaction  takes  place  at  a  much  lower  temperature  than  in  the 
previous  process  with  KOH,  and  the  losses  by  dissociation  of 
NH3  and  volatilization  of  the  cyanide  are  consequently  smaller. 
It  probably  takes  place  in  two  stages,  forming  sodamide  as  an 
intermediate  product: 

(1)  NH3  +  Na  =  NaNH2  +  H  (at  300°  to  400°  C). 
(2)  NaNH2  +  C  =  NaCN  +  H2  (at  dull  red  heat). 

In  a  modification  of  this  method  used  by  the  Deutsche  Gold 
and  Silber  Scheide-Anstalt,  metallic  sodium  is  melted  with  car- 
bonaceous matter  in  a  crucible,  and  then  ammonia  is  led  in  at 
400°  C. — 600°  C.;  this  forms  disodium  cyanamide: 

Na2  +  C  +  2NH3  =  Na2CN2  +  3H2. 

By  then  raising  the  temperature  to  700-800°  C.,  the  excess  of  C. 
interacts,  forming  sodium  cyanide : 

Na2CN2  +  C  =2NaCN; 
the  whole  operation  being  conducted  in  the  same  crucible 


MANUFACTURE    OF    CYANIDE  131 

Methods  have  also  been  proposed  by  J.  Mactear,  H.  C.  Wol- 
tereck,  and  others,  in  which  cyanogen  compounds  are  produced 
by  the  action  of  ammonia  gas  on  gaseous  carbon  compounds  at  a 
high  temperature. 

In  Mactear's  method  (Brit,  patent,  No.  5037,  of  1899)  the 
reaction  2NH;}  +  co  =  NH4CN  +  H2O 

is  supposed  to  take  place  in  a  closed  chamber  at  1800°  to  2000°  F., 
the  products  being  condensed  and  absorbed  in  alkali  hydrate  and 
the  ammonia  liberated  for  reuse.  Instead  of  CO,  a  mixture  of 
CO  with  N  and  H  (producer  gas)  may  be  used. 

In  Woltereck's  method  (Brit,  patent,  No.  19,804,  of  1902) 
"perfectly  dry  ammonia  and  a  volatilized  or  gaseous  carbon 
compound,  also  perfectly  dry,  are  passed  together  with  hydro- 
gen, in  equal  volumes,  over  a  strongly  heated  catalytic  agent, 
such  as  platinized  pumice.  One  volume  of  NH3  and  two  volumes 
of  'water-gas'  (CO  -f  H2)  make  a  convenient  mixture.  The 
HCN  produced  is  absorbed  in  an  alkaline  solution." 

Cyanide  has  also  been  made  from  the  trimethylamine  (CH3)3N 
obtained  by  the  distillation  of  beet-root  molasses  at  a  high  tem- 
perature. This,  at  a  red  heat,  decomposes,  giving  NH3,  HCN,  and  H. 

Another  source  of  cyanogen  compounds  is  the  crude  illumi- 
nating gas  from  the  distillation  of  coal.  In  Knublauch's  method 
(Brit,  patent,  No.  15,164,  of  1887)  the  gas  is  passed  through  a 
solution  of  an  alkali  or  alkaline  earth  containing  ferrous  hydrate 
in  suspension.  The  gas  carries  with  it  ammonium  cyanide  and 
thiocyanate,  which  are  absorbed  by  the  mixture  and  converted 
into  ferrocyanide. 

In  Rowland's  process  (U.  S.  patent,  No.  465,600,  of  1891)  the 
gas  is  passed  through  a  solution  of  an  iron  salt,  thus  forming 
ammonium  ferrocyanide.  This  is  converted  into  the  calcium  salt 
by  boiling  with  lime.  The  calcium  ferrocyanide  may  then  be  con- 
verted into  the  required  alkali  ferrocyanide  by  decomposing  with 
an  alkaline  carbonate. 

Bueb's  process  (Brit,  patent,  No.  9075,  of  1898)  is  a  modi- 
fication of  the  above,  in  which  the  cyanogen  is  separated  in  the 
form  of  an  insoluble  double  compound  by  using  a  concentrated 
iron  solution  (FeSO4) ;  the  reactions  said  to  take  place  are : 

FeSO4  +  HaS  +  2NH3  =  FeS 
2FeS  +  6NH4CN  =  (NH4)2Fe2(CN)6 


132  THE  CYANIDE  HANDBOOK 

The  insoluble  product,  known  as  "cyanide  mud,"  is  then 
treated  to  obtain  marketable  cyanogen  compounds. 

Many  other  modifications  have  been  suggested. 

Cyanides  may  also  be  obtained  by  desulphurizing  thiocyanates 
by  means  of  iron,  or  by  zinc  and  carbon. 


PART  III 

PREPARATORY  TREATMENT  OF  ORE  FOR  CYANIDING 

ONLY  a  brief  outline  can  be  given  here  of  the  mechanical 
principles  and  processes  which  form  a  necessary  preliminary  to 
cyanide  treatment  or  are  involved  in  the  carrying  out  of  the  process 
itself.  Details  of  the  construction  and  mode  of  action  of  the 
machines  used  will  be  found  in  any  text-book  of  metallurgy,  and 
much  information  on  these  points  is  usually  given  in  the  cata- 
logues supplied  by  the  makers. 

Whatever  metallurgical  process  is  to  be  adopted,  it  is  evident 
that  the  ore  as  taken  from  the  mine  will  require  to  undergo  a 
certain  amount  of  crushing  before  its  valuable  content  can  be 
extracted,  so  that  much  of  what  follows  does  not  specifically 
concern  the  cyanide  process.  We  shall  endeavor,  however,  to 
point  out  more  particularly  those  considerations  in  the  preparatory 
treatment  which  have  a  direct  bearing  on  subsequent  cyanide 
work. 


SECTION  I 

CRUSHING  MACHINERY 

(A)    ROCK-BREAKERS 

THE  reduction  of  an  ore  to  particles  of  a  size  suitable  for  any 
metallurgical  process  is  almost  always  carried  out  in  at  least  two 
stages,  for  which  different  types  of  machines  are  required.  These 
may  be  distinguished,  somewhat  arbitrarily,  as  Crushing  and 
Grinding.  In  the  first,  or  crushing,  stage,  the  ore  is  broken  by  a 
succession  of  blows  delivered  at  intervals  by  a  hard  moving  body, 
such  as  the  jaw  of  a  rock-breaker  or  the  shoe  of  a  stamp;  the  rock 
being  crushed  against  another  (generally  stationary)  hard  body, 
as  the  die  of  the  stamp  battery.  In  the  grinding  process  the 
comparatively  coarse  lumps  produced  by  crushing  are  pressed 
more  or  less  continuously  between  two  hard  surfaces  to  reduce 
them  to  a  smaller  size,  although  in  many  machines  (e.g.,  Gates 
crusher,  Ball  mill,  Tube  mill,  etc.),  both  actions  go  on  to  some 
extent  simultaneously.  For  economical  work,  it  may  be  stated 
as  a  nearly  universal  rule  that  crushing  must  precede  grinding, 
and  further,  that  separate  machines  should  be  used  for  different 
stages  of  crushing. 

The  first,  or  coarse,  crushing  is  carried  out  in  a  machine  known 
as  a  rock-breaker,  the  object  of  which  is  to  break  the  ore  as  it 
comes  from  the  mine,  which  'may  be  in  pieces  the  size  of  a  man's 
head  or  larger,  to  lumps  of  J  in.  to  J  in.  diameter,  suitable  for 
further  crushing  in  stamps  or  other  fine  crushers. 

The  rock-breakers  in  general  use  are  of  two  types:  (1)  those 
with  a  fixed  and  movable  jaw,  the  opening  between  which  is 
regulated  as  required,  such  as  the  Blake,  Blake-Marsden,  and 
Dodge  crushers;  (2)  those  with  a  gyrating  vertical  shaft,  work- 
ing against  plates  on  a  stationary  circular  shell  surrounding  the 
shaft,  as  in  the  Gates  and  Comet  crushers. 

In  the  first  type  (jaw  crushers)  the  fixed  and  movable  jaws 
are  inclined  at  an  angle  to  one  another,  the  smaller  opening  being 

135 


136  THE  CYANIDE.  HANDBOOK 

at  the  bottom.  The  ore  is  fed  in  at  the  top,  between  the  jaws. 
When  the  machine  is  at  work,  the  movable  jaw  rapidly  advances 
and  recedes  about  half  an  inch,  so  that  the  rock  gradually  slips 
down  and  is  crushed  between  the  jaws,  which  are  faced  with 
removable  plates  of  hard  steel.  The  Dodge  crusher  is  said  to 
be  suitable  for  somewhat  finer  crushing  than  the  Blake.  (Fig.  1.) 

In  the  second  type  (gyratory  crushers),  the  top  end  of  the 
shaft  is  usually  pivoted,  while  the  bottom  describes  a  circle.  A 
conical  piece  of  chilled  iron  or  steel  (breaking  head)  is  fitted  to 
the  shaft,  the  surface  of  which  is  inclined  at  an  angle  to  the  crush- 
ing faces  fixed  to  the  shell  or  hopper  surrounding  the  shaft.  As 
the  shaft  gyrates,  the  surface  of  the  breaking  head  alternately 
advances  toward  and  recedes  from  the  fixed  crushing  faces,  thus 
performing  the  same  functions  as  the  movable  jaw  in  the  jaw 
crushers.  The  crushing  surfaces  are  generally  corrugated,  and 
are  composed  of  chilled  iron,  chrome  steel,  manganese  steel,  or 
some  similar  material  combining  hardness  and  toughness.  (Fig.  2.) 
In  a  typical  case,  a  Blake  rock-breaker  will  crush  300  tons  of 
rock  in  24  hours  to  1  J-in.  size,  running  at  250  r.p.m.  and  requiring 
14  h.p.1 

The  accompanying  illustration,  Fig.  1,  shows  a  slightly 
modified  form  of  Blake  crusher  manufactured  by  Hadfield's 
Steel  Foundry  Co.,  of  Sheffield,  England.  The  rock  is  broken 
between  a  fixed  jaw  plate  and  a  movable  jaw  plate  actuated  by  a 
powerful  toggle  movement  communicated  to  it  from  the  driving 
pulley  through  an  eccentric  shaft  and  pitman. 

Fig.  2  illustrates  the  Gates  rock  and  ore  breaker  (Style  K), 
one  of  the  gyratory  type  manufactured  by  the  Allis  Chalmers 
Company,  of  Milwaukee.  The  main  shaft  (25)  is  suspended  in 
the  upper  part  from  spider  arms  (44)  that  span  the  top  of  the 
opening,  and  gyrates  without  revolving,  in  such  a  way  that  the 
ore  is  crushed  between  the  concave  shell  (19)  and  a  removable 
block  or  "head"  (18).  This  head  has  a  circular  and  rolling 
movement,  and  approaches  successively  every  point  in  the 
interior  of  the  throat,  owing  to  the  movement  of  the  lower  end 
of  the  axis  of  the  shaft  around  a  small  circle.  The  rock  is 
broken  rather  than  crushed.  It  falls  on  an  inclined  diaphragm 
which  protects  the  eccentric  and  gear,  and  thence  passes  to 
the  discharge  spout  (32).  The  main  shaft  is  adjustable, 

1  Rose,  "  Metallurgy  of  Gold,"  4th  edition,  p.  103. 


CRUSHING   MACHINERY 


137 


and  can  be  raised   or  lowered  to  regulate  the  size  of  product 
required. 


FIG.  1.  —  Modified  Blake  Crusher. 

(B)  STAMPS 

The  finer  crushing  of  gold  ores  is  almost  always  performed 
by  means  of  stamps,  except  in  cases  (1)  where  dry  crushing  is 
desirable,  or  (2)  where  the  ore  is  unusually  soft.  In  modern  prac- 
tice, crushing  with  stamps  is  frequently  followed  by  grinding  in 
pans  or  tube  mills,  as  described  below.  The  stamps  consist  of 
sets  (usually  five  in  each  set)  of  heavy  iron  hammers,  700  to 
1250  Ib.  in  weight.  Each  stamp  has  a  vertical  iron  rod  (stem), 
provided  at  the  lower  end  with  a  cylindrical  block  of  cast  iron 
(head),  into  which  the  stem  fits.  The  lower  end  of  the  head  has 


138 


THE  CYANIDE  HANDBOOK 


a  socket  to  receive  a  replaceable  block  of  hard  iron  (shoe)  which 
forms  the  crushing  surface.  The  stamps  are  alternately  raised 
and  dropped  by  means  of  a  horizontal  cam-shaft.  As  the  shaft 


FIG.  2.  —  Gates  Rock  and  Ore  Breaker. 

revolves,  the  cams  (set  at  different  angles  on  the  shaft)  strike 
against  a  block  (tappet)  fixed  to  the  upper  part  of  the  stem,  so 
that  the  stamp  is  raised  a  few  inches  as  the  cam  revolves,  and 


CRUSHING   MACHINERY 


139 


drops  by  its  own  weight  when  the  point  of  the  cam  passes  its 
highest  position.  The  cams  are  set  in  such  a  way  on  the  shaft 
that  each  stamp  is  lifted  and  dropped  in  succession,  in  a  par- 


FIG.  3.  —  Elevation  of  10-stamp  Battery,  showing  Mortar  Box,  etc.    [Eraser 

and  Chalmers.] 

ticular  order.  As  the  stamp  falls,  the  lower  surface  of  the  shoe 
strikes  the  layer  of  ore  resting  on  a  hard  iron  or  steel  block  (die), 
which  thus  acts  as  an  anvil.  The  dies  corresponding  to  each  set 


140 


THE  CYANIDE   HANDBOOK 


of  five  stamps  are  set  in  an  oblong  cast-iron  box  (mortar-box). 
(See  Fig.  7.)      The  ore  is  fed  in  on  one  side  of  the  row  of  stamps, 


and  discharged  on  the  other  side  through  a  screen  fitted  to  an 
opening  in  the  mortar-box,  the  lower  edge  of  which  is  a  few 
inches  above  the  top  of  the  die.  (Figs.  3,  4,  5,  6.) 


CRUSHING   MACHINERY  141 

After  leaving  the  rock-breakers  and  before  passing  to  the 
stamps  or  other  mill,  the  ore  is  generally  sifted,  through  a  coarse 
screen  consisting  of  parallel  steel  bars,  known  as  a  ''grizzly" 
(see  Fig.  16),  the  oversize  returning  to  rock-breakers.  When 
stamps  are  used,  as  is  generally  the  case,  for  wet  crushing,  a 
stream  of  water  is  fed  into  the  mortar-box  along  with  the  ore, 
and  a  further  supply  of  water  is  usually  added,  outside  the  battery, 


FIG.  5.  —  New  Blanton  Cam.     [Fraser  and  Chalmers.] 


FIG.  6.  —  Cam  Shaft,  showing  5  Cams  in  Position.   [Fras3r  and  Chalmers.] 

to  wash  away  the  ore  as  it  passes  through  the  screens.  The 
fineness  to  which  the  ore  is  crushed,  which  is  the  principal  point 
of  interest  with  regard  to  subsequent  cyanide  treatment,  depends 
chiefly  on  the  (1)  size  of  openings  in  screen  used  in  mortar-box; 
(2)  relative  amount  of  ore  and  water  fed  in;  (3)  hight  of  discharge 
above  dies;  (4)  hight  of  drop  of  stamps;  (5)  rate  at  which  ore 
is  fed  into  mortar-box. 

Where  the  object  is  to  treat  as  much  of  the  product  as  possible 
by  percolation,  it  is  of  course  desirable  to  crush  the  ore  only  so 
fine  as  may  be  necessary  to  render  a  sufficient  percentage  of  the 


142 


THE  CYANIDE   HANDBOOK 


values  accessible  to  the  solvent;  this  will  be  attained  by  (1)  using 
a  somewhat  coarse  screen;  (2)  using  much  water  in  proportion  to 
ore,  so  as  to  wash  out  the  crushed  ore  as  soon  as  it  is  reduced 
to  the  required  size;  (3)  having  the  discharge  as  close  as  possible 
to  the  top  of  the  dies,  to  avoid  crushed  ore  being  repeatedly 


liu.   /.  —  Section   of  Mortar-box. 
[Fraser  and  Chalmers.] 

thrown  back  under  the  stamps;  (4)  using  heavy  stamps  running 
at  a  high  speed,  with  the  least  hight  of  drop  possible  in  practice; 
this  results  in  a  maximum  quantity  of  material  being  crushed  for 
a  given  expenditure  of  power;  (5)  keeping  the  rate  of  feed  low, 
so  as  to  avoid  banking  of  the  ore  against  the  screen,  which  would 
lead  to  unnecessary  recrushing  of  the  same  material. 

In  many  cases,  however,  it  is  more  advantageous  to  crush 
finer,  even  although  the  output  of  ore  per  stamp  may  be  reduced, 


CRUSHING   MACHINERY  143 

as  the  extraction,  both  by  cyanide  and  by  amalgamation,  is  usually 
greater  the  finer  the  state  of  division  to  which  the  ore  particles 
are  reduced.  Frequently  the  ore  contains  two  constituents  of 
different  degrees  of  hardness,  quartz  and  pyrites,  one  of  which 
carries  practically  the  whole  of  the  value.  If,  as  is  the  case  on 
the  Rand,  the  quartz  is  barren,  while  the  whole  of  the  gold  is 
associated  with  or  imbedded  in  the  pyrites,  it  would  seem  that 
the  best  method  would  be  to  crush  coarsely  at  first,  then  separate 
the  pyrites  by  some  form  of  concentration  or  other  mechanical 
means,  and  regrind  the  pyritic  portion  alone  as  finely  as  pos- 
sible. 

In  general,  it  may  be  said  that  when  the  ore  is  to  be  sub- 
sequently treated  by  cyanide,  less  trouble  and  loss  will  be  caused 
by  crushing  too  fine  than  by  crushing  too  coarse,  since  in  the  coarse 
particles  the  gold  or  silver  is  absolutely  inaccessible  to  the  solvent; 
whereas  the  difficulties  in  the  way  of  the  mechanical  handling 
of  slimes  in  order  to  extract  their  dissolved  values  have  been 
greatly  reduced  if  not  entirely  overcome  by  modern  methods. 
Another  point  of  great  importance  for  cyanide  work  is  uniformity 
of  -the  mill  product,  both  as  regards  fineness  of  the  ore  particles, 
and  as  to  proportion  of  water.  The  whole  system  of  treatment 
must  be  regulated  in  accordance  with  these  factors,  and  any 
unforeseen  variation  may  give  rise  to  bad  extractions  and  heavy 
losses.  Where  "  spitzlutten  "  (see  below)  are  used  for  separation 
of  sands  and  slimes,  they  are  arranged  to  give  the  required  product 
by  regulating  the  size  of  outlet,  etc.,  and  any  variation  in  the  ratio 
of  ore  to  water  will  result  either  in  slime  passing  into  the  sand 
tanks  or  in  fine  sand  being  carried  away  with  the  slime.  It  is 
obvious  that  the  whole  metallurgical  treatment  should  be  re- 
garded as  one  problem,  and  the  preliminary  operations  of  crush- 
ing and  grinding  should  be  made  subservient  to  the  extraction 
processes  which  are  to  follow,  and  not  carried  out  merely  with  a 
view  to  passing  through  the  maximum  quantity  of  ore  in  a  given 
time. 

As  an  example  of  typical  stamp  battery  practice  under  modern 
conditions,  the  following  is  given,  on  the  authority  of  T.  Roskelley,1 
as  having  been  used  in  the  crushing  of  banket  ore  at  the  Robin- 
son Deep  G.  M.  Co.'s  battery: 

i  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  III,  338. 


144 


THE  CYANIDE   HANDBOOK 


Standard   Screen 
Used 

Hight  of  Drop: 
Inches 

Speed:  Drops 
per  Minute 

Water  Used 
per  Ton 
Crushed 

Tons  Crushed 
per  Stamp  per 
24  Hours 

Slimes  Produced 
Per  Cent. 

600 

8i 

96 

6 

5.45 

25.4 

700 

81 

96 

6 

5.28 

29.0 

900 

81 

96 

61 

5.07 

31.8 

1000 

71 

100 

7 

5.06 

35.3 

1200 

74 

100 

74 

4.95 

35.0 

Fall  of  Plates  =  1  fa  in.  per  foot. 
Hight  of  discharge  =  2 1  in. 

Other  authorities  (e.g.,  F.  Alexander)  recommend  a  greater 
hight  of  discharge,  such  as  6  or  8  in.,  which,  with  other  conditions 
remaining  the  same,  would  result  in  a  finer  product  and  dimin- 
ished output. 

A  full  account  of  this  subject  will  be  found  in  the  following 
papers,  to  which  reference  should  be  made  for  further  details  as 
to  mill  practice  and  its  effect  on  cyanide  treatment: 

"The  Stamp  Milling  of  Gold  Ores  in  its  relation  to  Cyaniding," 
by  E.  H.  Johnson,  in  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South 
Africa,"  II,  176  (1897). 

"  Notes  on  the  Common  Practice  of  Quartz  Milling  on  the 
Rand,"  by  F.  Alexander.  Ibid.,  Ill,  298  (1903). 

Much  useful  information  as  to  the  effectiveness  of  the  crush- 
ing with  a  view  to  cyanide  treatment  may  be  obtained  by  sifting 
a  sample  of  the  product  through  a  number  of  screens  of  varying 
mesh,  and  assaying  the  portions  passing  through  successive 
screens,  similar  tests  being  also  made  on  the  residues  after  cyanide 
treatment.  When  the  battery  pulp,  before  cyanide  treatment, 
is  examined  in  this  way,  it  is  generally  found  that  one  portion 
of  the  crushed  ore  is  richer  than  another,  and  frequently  that 
the  finer  products  are  the  richer.  With  the  residues  after  cyanide, 
however,  it  is  almost  invariably  the  case  that  the  coarser  portions 
are  the  richer,  showing  that  finer  crushing  of  this  part  of  the  ore 
would  result  in  higher  extraction.1  Finer  crushing  usually  results 
also  in  improved  amalgamation,  not  only  because  more  gold  is 
brought  into  actual  contact  with  the  mercury,  but  because  me- 

1  Tests  on  these  lines  made  weekly  for  a  number  of  years  at  the  Redjang 
Lebong  mine,  Sumatra,  showed  scarcely  an  exception  to  this  rule,  both  as  regards 
gold  and  silver  values. 


CRUSHING   MACHINERY  145 

chanical  losses  of  amalgam,  due  to  the  passage  of  coarse  material 
over  the  surface  of  the  plates,  are  much  lessened.  Any  amalgam 
carried  off  in  this  way  is  practically  lost,  as  but  little  dissolves 
in  cyanide  during  the  time  of  treatment  usually  given.  This 
matter  will  be  further  discussed  under  amalgamation.  In  this 
connection  the  following  remarks  by  P.  S.  Tavener l  are  very 
much  to  the  point: 

"  Would  it  not  be  better  to  take  the  pulp  leaving  the  mortar- 
boxes  and  pass  it  direct  to  a  grinding  machine,  or  to  separate,  by 
means  of  classifiers,  the  particles  requiring  regrinding  before 
amalgamation  or  afterwards?  It  would  appear  to  be  better  to 
do  so  before,  for  if  done  afterward  the  reground  portion  would 
have  to  pass  over  the  plates  for  a  second  time.  Is  it  not  likely 
that  it  is  the  coarser  particles  that  help  to  scour  the  plates?" 

As  the  stamp  mill  is  not  adapted  for  crushing  effectively  and 
economically  to  a  very  high  degree  of  fineness,  it  is  desirable  to 
pass  a  part  at  least  of  the  product  from  the  battery  through 
some  grinding  machine;  hence 'the  modern  practice  is  to  use  the 
stamp  battery  for  comparatively  coarse  crushing,  supplementing 
it  by  one  or  other  of  the  grinding  machines  described  in  the 
following  section. 

i "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  III,  329. 


SECTION   II 

GRINDING   MACHINERY 

THE  type  of  machine  to  be  used  for  grinding  will  depend  largely 
on  the  hardness  and  general  character  of  the  ore  and  on  the  treat- 
ment which  it  has  previously  undergone.  In  some  cases  the  ore 
may  pass  direct  from  rock-breakers  to  the  grinding  machines, 
but  this  can  in  general  only  be  done  with  comparatively  soft 
material,  or  in  cases  where  the  ore  is  to  be  crushed  dry.  The 
grinding  machines  principally  used  in  connection  with  cyaniding 
are  rolls,  grinding  pans,  ball  mills,  and  tube  mills. 

(A)  ROLLS 

These  consist  of  two  parallel  cylinders  with  their  axes  placed 
horizontally.  (See  Fig.  8.)  The  tires,  or  crushing  faces,  are  of 
forged  steel  or  chilled  iron,  usually  smooth,  and  are  replaceable 
when  worn.  The  rolls  are  mounted  so  that  they  revolve  at  a  dis- 
tance of  f  to  -gV  in.  apart,  according  to  the  fineness  of  the  product 
required.  The  usual  sizes  are  12  to  16  in.  across  the  face,  and  22 
to  40  in.  diameter.  The  product  obtained  varies  from  -|  in.  size 
to  about  70-mesh,  depending  on  the  distance  between  the  crush- 
ing faces  of  the  two  rolls.  They  are  used  almost  exclusively  for 
dry  crushing,  the  ore  being  fed  between  the  revolving  rolls  by 
means  of  a  hopper.  After  leaving  the  rock-breakers  and  before 
reaching  the  rolls,  the  ore  is  passed  over  screens,  and  the  over- 
size, too  large  to  be  fed  direct  to  the  rolls,  is  returned  to  the  rock- 
breakers.  In  some  cases  a  succession  of  rolls  is  used  to  reduce  the 
ore  to  varying  degrees  of  fineness,  with  suitable  screens  between 
each  pair.  The  speed  may  be  from  60  to  150  r.p.m.,  the  velocity 
at  the  circumference  being  (say)  750  to  1000  feet  per  minute.  In 
some  cases  the  two  rolls  are  made  to  revolve  at  different  velocities. 
A  detailed  account  of  modern  practice  with  rolls  will  be  found  in 
a  paper  by  P.  Argall,  "Sampling  and  Dry  Crushing  in  Colorado."  1 
(See  Fig.  9.) 

1  Trans.  I.  M.  M.  X,  234-273. 
146 


GRINDING   MACHINERY 


147 


In  general,  H  may  be  stated  that  rolls  are  the  most  suitable 
machines  for  dry  crushing  where  the  object  is  to  produce  as  little 
fine  dust  as  possible;  when  set  to  a  particular  opening,  they  pro- 


FIG.  8.  —  Smooth  Crushing  Rolls,  manufactured  by  Hadfield's  Steel  Foundry 
Co.,  Sheffield.  The  frames  are  of  toughened  cast  steel  and  the  shells 
(crushing  surfaces  of  the  rolls)  are  of  "Era"  manganese  steel  or,  when 
used  for  fine  crushing,  of  best  quality  toughened  cast  steel.  The  rolls 
are  driven  by  means  of  belts  running  on  two  heavy  fly-wheel  pulleys. 

duce  a  minimum  of  material  crushed  to  a  greater  degree  of  fine- 
ness. They  are  not  usually  suitable  for  very  coarse  or  very  fine 
crushing;  the  material  fed  to  the  rolls  should  have  been  pre- 
viously reduced  at  least  to  2-in.  size  by  rock-breakers,  and  if 
very  fine  grinding  is  necessary,  the  product  from  the  last  set  of 
rolls  should  be  passed  to  grinding  pans  or  tube  mills.  Screen 
analyses  of  the  product  obtained  by  rolls  on  Cripple  Creek  ore 
are  given  by  Argall  (loc.  cit.,  pp.  269,  270),  as  follows: 

I.   Size  of  opening  =  .0212  in.  (andesitic  and  granite  ores). 


Remaining  on 


Ore 

n                40-mesh     
'       40  to  60-mesh     . 

(a) 
Per  cent. 
21 

17 

(ft) 

Per  cent. 
13 

20 

W 

Per  cent. 
31 

16 

'     60  to  120-mesh     . 

41 

54 

44 

'   120  to  200-mesh     

15 

12 

6 

Passinsr  200-mesh 

6 

1 

3 

148 


THE  CYANIDE   HANDBOOK 

II.    Size  of  opening  =  .02  in.  (base  ore). 
Remaining  on 


n                50-mesh 

(<*) 

Per  cent. 

31.5 

(«) 

Per  cent. 

32.5 

'     50  to  100-mesh     . 
'   100  to  200-mesh 

26 
16.5 

26 
16.5 

Passing  200-mesh     . 

26 

25 

It  is  seldom  advantageous  to  use  rolls  for  crushing  finer  than 
about  30-mesh.     When  ore  requires  to  be  roasted  previous  to 


FIG.  9.  —  Argall  Rolls,  furnished  by  Fraser  and  Chalmers.  These  are  belt- 
driven,  and  one  roll  is  fixed  while  the  other  is  movable.  The  bearings 
of  the  movable  roll  are  connected  by  a  heavy  cast-iron  yoke,  insuring 
that  the  face  of  this  roll  will  always  remain  parallel  to  the  face  of  the 
fixed  roll. 

cyanide  treatment,  it  is  very  generally  crushed  by  means  of  rolls, 
as  it  is  desirable  to  avoid  producing  an  excessive  quantity  of  fine 
material.  In  some  cases  the  whole  or  part  of  the  roasted  product 
is  ground  finer  before  undergoing  treatment. 

(B)    GRINDING  MILLS 

These  are  of  many  types.  Those  used  in  the  process  of  pan- 
amalgamation  consist  essentially  of  a  heavy  shoe  or  muller, 
revolving  about  a  vertical  axis,  the  ore  being  ground  between 
the  under  surface  of  this  muller  and  the  bottom  of  the  pan. 


GRINDING   MACHINERY 


149 


Descriptions  of  these  machines  will  be  found  in  any  work  on  the 
metallurgy  of  silver.1  The  bottom  of  the  pan  is  lined  with  replace- 
able cast-iron  "  dies."  The  muller  revolves  at  about  70  r.p.m., 
and  the  ore,  previously  crushed  to  a  sufficient  degree  of  fineness, 


FIG.  10.  —  Evans- Waddell  Chilian  Mill,  manufactured  by  Fraser  and  Chal- 
mers. This  machine  consists  of  three  crushing  rollers  mounted  on  hori- 
zontal arms,  connected  with  a  central  vertical  driving-shaft,  the  latter 
being  driven  by  means  of  a  horizontal  pinion-shaft  and  bevel-gear  at- 
tached to  the  lower  part  of  the  vertical  shaft.  The  mortar  or  pan  is 
lined  inside  with  hard  iron  wearing-plates,  and  the  die-ring  and  roller 
shells  are  of  the  best  quality  forged  steel.  There  are  six  screen  openings 
for  discharging  the  crushed  material. 

is  fed  in  with  sufficient  water  to  make  a  thick  pulp;  after  the  ore 
has  been  ground  for  some  hours,  mercury  is  added  and  the  grind- 
ing is  continued,  sometimes  with  the  addition  of  other  chemicals. 
Other  forms  of  grinding  machines  which  are  in  use,  either 
with  or  without  the  addition  of  mercury,  may  here  be  mentioned. 


i  See  also  Rose,  loc.  cit.,  pp.  169-173. 


150  THE  CYANIDE  HANDBOOK 

Among  the  best  known  are  the  Arrastra,  Chilian  mill,  Griffin 
mill,  Bryan  mill,  and  Huntington  mill.  These  machines,  although 
of.  widely  different  construction  in  detail,  have  certain  features 
in  common.  In  all  of  them  the  grinding  part  is  made  to  revolve 
about  a  central  vertical  shaft,  and  acts  against  a  circular  or 
annular  surface  forming  the  bottom  or  side  of  the  machine. 

The  Arrastra,  probably  the  oldest  and  most  primitive  machine 
used  in  ore  treatment,  is  still  employed  to  a  large  extent  in  some 
parts  of  America.  It  consists  of  a  bed  or  pavement  of  hard  stone, 
with  a  wooden  shaft  set  in  the  center,  bearing  a  horizontal  revol- 
ving arm  or  arms,  to  which  heavy  stones  are  attached;  the  ore, 
previously  broken  in  small  pieces,  is  ground  between  the  revolving 
stone  and  the  pavement.  It  is  capable  of  very  fine  grinding, 
but  the  output  is  of  course  very  small. 

The  Chilian  mill  consists  of  large  wheels  or  rollers,  which 
may  be  as  much  as  8  ft.  in  diameter  and  6  in.  wide,  revolving 
on  horizontal  axes  in  an  annular  trough  or  mortar.  (Fig.  10.) 
The  Bryan  mill  is  of  similar  construction,  consisting  of  three 
rollers  mounted  on  horizontal  axles,  which  revolve  about  the 
central  axis  of  the  machine.  The  rollers  run  in  an  annular 
mortar  lined  with  segmental  steel  dies;  the  central  shaft  makes 
about  30  r.p.m.,  the  pulp  at  the  periphery  running  round  at  over 
300  feet  per  minute.  The  capacity  of  a  4-foot  mill  is  about  15  to 
20  tons  of  quartz  ore  per  day  through  a  40-mesh  screen.1  These 
mills  are  suitable  for  both  hard  and  soft  ores. 

The  Huntington  mill  is  somewhat  similar,  but  the  rollers  are 
mounted  on  vertical  axles  suspended  from  a  circular  horizontal 
carrier  revolving  about  a  central  vertical  axis.  The  grinding  is 
due  to  the  pressure  of  these  rollers  against  the  sides  of  the  mill, 
which  are  lined  with  an  annular  replaceable  die  of  steel  or  cast 
iron.  Above  this  is  an  annular  screen  for  the  discharge  of  the 
crushed  ore.  A  hopper  is  also  placed  at  the  side  of  the  mill  for 
feeding  in  the  ore,  which  should  be  previously  crushed  to  nut  size 
in  a  rock-breaker.  The  rollers  are  suspended  about  one  inch 
from  the  bottom  of  the  pan,  and  being  free  to  swing  radially 
as  well  as  to  revolve  on  their  own  axes,  they  are  driven  by  cen- 
trifugal force  against  the  ring-die  when  the  carrier  revolves.  The 
speed  is  45  to  90  r.p.m.,  usual  diameter  5  ft.  This  machine  is 
particularly  suitable  for  soft  ores,  which  it  crushes  much  more 

1  Rose,  loc.  cit.,  p.  165. 


GRINDING   MACHINERY 


151 


effectively  than  stamps,  and  owing  to  the  freer  discharge  it  pro- 
duces less  slime  than  the  latter.  Enough  water  is  added  in  the 
feed  hopper  to  make  a  thick  pulp,  and  in  cases  where  the  mill  is 


FIG.  11.  —  Improved  Huntington  Mill  manufactured  by  Fraser  and  Chalmers. 
It  is  claimed  that  this  mill  can  be  run  with  less  expenditure  of  power  per 
ton  of  ore  crushed  than  any  other  similar  mill.  The  ore  is  discharged 
through  the  screen  as  soon  as  it  is  crushed  fine  enough,  thus  avoiding 
the  production  of  slime  and  giving  a  product  very  suitable  for  concen- 
tration. 

to  be  used  as  an  amalgamating  machine,  from  17  to  25  Ibs.  of 
mercury  are  added,  forming  a  layer  at  the  bottom  just  beneath 
the  rollers.  The  cost  is  about  two-thirds  that  of  stamps  for  the 
same  crushing  capacity;  less  power  is  required  per  ton  crushed,1 
and  the  cost  of  repairs  and  renewals  is  less.  There  is  also  less 
floured  mercury  than  is  given  by  stamps  with  inside  amalgama- 
tion.2 (Figs.  11  and  12.) 

i  Tho  power  required  is  : 

For  mill  3^  ft.  diam.,  speed  90  r.p.m.,  4  h.p. 

5  "        "          "       70      "       6    " 

6  "        "          "       55      "        8    " 
2/feid.,  p.  161. 


152 


THE  CYANIDE  HANDBOOK 


(C)    BALL  MILLS 


These  consist  essentially  of  cylindrical  revolving  drums  con- 
taining a  number  of  steel  balls  of  various  sizes.  The  interior 
of  the  drum  is  lined  with  steel  plates,  arranged  so  that  a  portion 
of  each  projects  inward,  forming  a  shelf  which  has  the  effect  of 


FIG.  12.  —  Sectional  view  of  a  Huntington  Mill  as    made  by    Fraser   and 

Chalmers. 

raising  the  balls  and  dropping  them  during  the  rotation  of  the 
drum.  The  other  portion  of  the  lining  plates  is  perforated.  The 
ore  is  fed  in  through  a  hopper  at  one  end  of  the  drum,  and  is 
crushed  by  the  impact  of  the  balls  against  the  grinding  surfaces 
of  the  lining  and  against  each  other.  The  action  is  in  fact  a 
combination  of  crushing  and  grinding.  The  crushed  ore  passes 
through  the  perforations  to  a  set  of  inner  and  outer  sieves  con- 


GRINDING   MACHINERY  153 

centric  with  the  circumference  of  the  drum.  The  first  or  inner 
screens  consist  of  perforated  steel  plates  which  serve  to  protect 
the  outer  wire  screens.  The  oversize  returns  automatically  to  the 
interior  of  the  drum  through  openings  between  the  lining  plates. 
The  material  passing  the  sieves  goes  through  a  hopper  forming 
part  of  an  outer  casing  of  sheet  iron,  surrounding  the  revolving 
drum,  which  discharges  the  crushed  ore  at  the  bottom.  (Fig.  13.) 


FIG.  13.  —  Ball  Mill,  No.  8  size.     [From  photograph  furnished  by  Cyanide 

Plant  Supply  Co.] 

These  machines  may  be  used  either  for  wet  or  dry  crushing, 
but  are  more  commonly  used  for  the  latter  purpose.  Where  the 
object  is  to  crush  a  large  percentage  of  the  product  to  a  tolerably 
high  degree  of  fineness,  ball  mills  are  more  effective  than  stamps 
or  rolls.  Julian  and  Smart 1  state  that  ball  mills  of  the  Krupp- 
Grusonwerk  type  are  generally  preferable  to  rolls  or  stamps  for 
dry  crushing,  and  recommend  crushing  coarsely  in  the  first  in- 
stance, say  12  to  20  mesh,  and  passing  the  product  through  a 
second  machine  for  the  finer  grinding.  The  following  screen- 

1 "  Cyaniding  Gold  and  Silver  Ores,"  2d  edition.,  p  47. 


154  THE  CYANIDE   HANDBOOK 

analysis  given  by  the  same  authorities  (loc.  cit.,  p.  199)  will  serve 
to  illustrate  the  nature  of  the  product  obtained  by  crushing  in 
ball  mills.  An  ore  from  the  Kalgurli  mines,  West  Australia, 
fed  in  2^  in.  size  to  a  No.  5  Krupp  ball  mill  with  35-mesh  screens, 
gave  a  product : 

35  to    80-mesh 30  per  cent. 

80  to  120-mesh 30        " 

Passing  120-mesh 40        " 

Another  example  is  given  by  Dr.  Simon  ("Trans.  I.  M.  M." 
X,  290),  from  No.  4  Krupp  ball  mills,  crushing  dry  with  30-mesh 
screens,  on  ore  from  Norseman  Mine,  West  Australia: 

Remaining  on  30-mesh  0.6  per  cent 

30to40-mesh  .'. .  16.1 

40  to  60-mesh  17.1 

60  to  80-mesh  25.2 

Passing  80-mesh  41.0        " 

These  may  be  compared  with  the  figures  given  for  the  product 
obtained  by  crushing  with  rolls,  given  by  P.  Argall  for  Cripple 
Creek  ore  (see  above),  where  the  percentage  passing  120-mesh 
was  from  9  to  21  per  cent.  Where  ball  mills  are  used  for  wet 
crushing,  the  water  is  led  into  the  interior  of  the  drum  and  di- 
rected in  a  spray  against  the  sieves,  the  discharge  hopper  being 
arranged  as  a  spitzkasten,  for  separating  sands  and  slimes.  The 
power  required  is  8  or  9  h.p.  for  an  output  of  200-300  Ib.  per 
h.p.-hour,  crushing  to  40-mesh  (Argall,  loc.  cit.,  p.  296). 

Ball  mills  are  also  extensively  used  for  crushing  lime,  cement, 
slag,  and  other  materials,  and  sometimes  for  mixing  the  fluxes 
and  precipitate  from  the  zinc-boxes  previous  to  smelting. 

(D)    TUBE  MILLS 

These  machines,  which  have  been  very  extensively  introduced 
of  late  years  for  the  fine  grinding  of  ore  before  cyanide  treatment, 
consist  of  sheet  steel  drums  13  to  22  ft.  in  length,  having  an  in- 
ternal diameter  of  3  to  5  ft.  They  are  lined  internally  with  re- 
placeable blocks  of  some  hard  material,  such  as  hardened  steel 
or  "silex,"  and  the  remaining  space  is  generally  rather  more 
than  half  filled  with  rounded  flint  pebbles.  The  cylinder  is 
mounted  on  trunnions,  with  its  axis  slightly  inclined  downwards 
from  the  feed  to  the  discharge  end.  The  ore  or  battery  pulp, 


GRINDING   MACHINERY  155 

reduced  to  a  suitable  consistency  by  removal  of  superfluous  water 
by  means  of  spitz kasten  or  otherwise,  is  fed  in  by  means  of  a 
hopper  through  an  opening  in  one  of  the  ends  of  the  drum.  Dur- 
ing the  rotation  of  the  machine  the  pebbles  cling  to  the  lining 


FIG.  14.  —  Davidsen  Wet  Crushing  Tube  Mill.     Feed  end. 

for  some  distance  up  the  ascending  side,  and  then  drop  to  the 
bottom  of  the  drum,  crushing  the  ore  by  their  impact.  The 
crushed  ore  is  discharged  through  an  opening  at  the  opposite 
end  of  the  drum,  and  usually  passes  to  spitzlutten,  from  which 
the  coarser  product  is  returned  to  the  feed  end  of  the  mill  and 
reground.  (Figs.  14  atid  15.) 

To  obtain  the  maximum  efficiency  from  tube  mills,  great 
care  is  necessary  in  regulating  the  speed,  the  rate  of  feeding, 
consistency  c-f  pulp,  and  charge  of  pebbles.  According  to  W.  R. 
Dowling,1  the  tube  mills  of  the  Robinson  Deep  G.  M.  Co.  are  run 
at  a  speed  of  29  r.p.m.;  about  230  tons  of  sand  are  fed  to  each 
mill  per  24  hours;  the  pulp  should  be  as  thick  as  possible  (in  the 
case  cited  it  contains  about  40  per  cent,  of  water  to  60  per  cent, 
of  solids) ;  the  load  of  pebbles  is  rather  more  than  half  the  inter- 
nal volume  of  the  mill. 

The  nature  of  the  liners  is  also  a  matter  of  considerable  im- 
portance. It  appears  to  have  been  generally  found  that  "silex" 
linings  give  more  satisfactory  and  economical  results  than  man- 
ganese steel.  The  silex  consists  of  hard  flint  cut  in  blocks  about 
2J  in.  thick,  and  secured  to  the  inside  of  the  shell  by  a  setting  of 
Portland  cement.  Blocks  of  4  in.  have  been  used  and  are  con- 
siderably more  economical,  as  they  last  longer.  The  pebbles  are 

1  "  Tube  Mill  Practice,"  in  Journ.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa, 
VI,  308  (April,  1906). 


156 


THE  CYANIDE   HANDBOOK 


2  to  3  in.  in  diameter  and  are  mostly  imported  from  the  Danish 
coast,  but  in  South  Africa  the  practice  has  been  introduced  of 
using  pieces  of  the  banket  ore  itself  as  the  crushing  medium; 
lumps  3  to  6  in.  in  diameter  are  quickly  reduced  by  the  action 
of  the  mill  to  the  form  of  a  round  pebble.  The  size  of  pebbles 
required  seems  to  depend  on  the  size  of  the  product  to  be  crushed; 
the  finer  the  particles  entering  the  mill  the  smaller  the  pebbles 
needed. 


FIG.  15.  —  Davidsen  Wet  Crushing  Tube  Mill.     Discharge  end, 
nished  by  the  Cyanide  Plant  Supply  Co.] 


[Fur- 


The  feed  is  regulated  by  reducing  or  enlarging  the  discharge 
opening  of  the  spitz kasten  used  for  dewateririg  the  pulp  before 
it  enters  the  tube  mill.  According  to  Bowling  (toe.  ciL,  p.  310), 
"the  best  indication  that  a  tube  mill  is  being  given  a  sufficient 
feed  is  the  continual  presence  of  a  few  inches  of  sand  at  the  bottom 
of  the  dewatering  spitzkasten."  The  action  of  the  mill  is  thus 
described:  "The  thicker  the  pulp,  the  better  the  grinding  and 
the  less  the  wear  on  both  liners  and  pebbles,  since  the  sluggish 
pulp  clings  to  both  pebbles  and  liners  and  forms  a  layer  to  take 
the  blow  of  the  falling  and  the  abrasion  of  the  rolling  pebbles. 
The  clinging  action  of  the  thick  pulp  can  be  seen  at  the  discharge 
end  of  the  mill,  and  this  is  a  ready  means  of  telling  whether  the 
feed  is  of  approximately  the  right  consistency." 


GRINDING   MACHINERY 


157 


The  crushing  efficiency  of  a  tube  mill  is  generally  measured 
by  comparing  the  percentages  of  coarse  and  fine  sand  in  the  pulp 
fed  to  the  mill  and  in  the  product  delivered  by  it.  A  somewhat 
arbitrary  rule  is  to  take  the  sum  of  the  decrease  in  material 
remaining  on  60-mesh  and  the  increase  of  material  passing  90- 
mesh  as  representing  the  work  done  by  the  mill.  The  nature  of 
the  products  entering  and  leaving  the  tube  mill,  in  ordinary 
working  conditions,  is  shown  by  the  following  table  given  by 
Bowling  (loc.  cit.,  p.  313)  at  the  Robinson  Deep. 


Grade 

PULP  LEAVING  BATTERY 
(Entering  Tube  Mill) 

PULP  ENTERING  CYANIDE 
WORKS 
(From  Tube  Mill) 

WORK  DONE 

Per  Cent,  of 
Total  Wt. 

Tons 

Per  Cent,  of 
Total  Wt. 

Tons 

Per 
Cent. 

Tons 

Remaining  on  60-mesh 
60  to  90-mesh  
Passing  90-mesh  

28.66 
17.43 
53.91 

8,599 
5,230 
16,175 

5.28 

16.50 

78.22 

1,584 

4,951 
23,469 

23.38 

7,015 

24.31 

7,294 

100.00 

30,004 

100.40 

30,004 

47.69 

14,309 

30-mesh     
30  to  40-mesh     
40  to  60-mesh     
'  60  to  100-mesh     
100  to  150-mesh     

Before 
Tube  Milling 
Per  cent. 

5.32 
9.77 
15.94 
13.96 
12.29 

After 
Tube  Milling 
Per  cent. 
0.03 
0.12 
1.13 

7.43 
18.42 

150-mesh 

42.72 

72.87 

A  more  detailed  analysis  of  the  gradings  at  the  Waihi  mine, 
New  Zealand,  is  given  by  E.  G.  Banks: x 


Remaining  on 


Passing 

A  comparative  test  between  crushing  in  a  tube  mill  with 
gold  quartz  (Rand  banket  ore)  and  Danish  pebbles  is  given  by 
K.  L.  Graham,2  showing  results  slightly  in  favor  of  the  quartz. 
In  both  cases  the  mills  were  lined  with  silex  blocks,  6X6X4  in., 
laid  on  edge.  The  wear  on  the  linings  was  certainly  not  greater 
when  quartz  was  used.  The  results  of  a  month's  work  (January, 
1907)  are  given  as  follows: 

i  "  Trans.  A.  I.  M.  E,"  XIII,  p.  63  (Jan.,  1907). 

a  "  Journ.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  VII,  318  (April,  1907). 


158  THE  CYANIDE  HANDBOOK 

No.  1  MILL  No.  2  MILL 

Quartz  fed  171.5  tons.  Pebbles  10  tons. 

Entering:  Leaving:  Entering:  Leaving: 

Product:  per  cent.  per  cent.  per  cent.  per  cent. 

Remaining  on  60-mesh  68.68  9.73  68.68  11.32 

60  to  90-mesh  19.57  26.28  19.57  27.24 

Passing  90-mesh  11.75  63.99  11.75  61.44 

The  lumps  of  ore,  up  to  4^  in.  diameter,  are  introduced  by 
means  of  a  feeder  consisting  of  a  hopper  leading  to  a  bent  cast-iron 
tube,  5  in.  in  diameter  at  the  narrowest  part,  and  passing  into 
the  hollow  trunnion  at  the  feed  end  of  the  mill.  The  pulp  from 
the  spitzkasten  is  fed  into  the  same  tube  near  the  bottom,  oppo- 
site the  outlet  of  the  bend  (where  it  enters  the  trunnion). 

At  Waihi,  New  Zealand,  liners  have  been  used  consisting  of 
cast-iron  frames  divided  into  square  compartments  about  3^  in. 
deep;  these  are  filled  in  with  hard  quartz  or  quartzite,  embedded 
in  Portland  cement  mixed  with  ground  flint  fragments.  These 
"honeycomb  liners"  appear  to  be  as  efficient  as  silex  or  quartzite 
blocks,  and  cost  much  less.  At  the  Waihi,  4  mills,  22  ft.  in  length, 
are  run  at  27.5  r.p.m.  Each  mill  has  a  load  of  5.5  tons  of  flints 
and  requires  50  h.p.  to  operate  it. 


SECTION   III 

MECHANICAL  HANDLING  OF  MATERIAL  FOR  CYANIDE 

TREATMENT 

DURING  the  early  years  of  the  cyanide  process  it  was  applied 
almost  exclusively  to  the  treatment  of  accumulations  of  already 
crushed  ore,  which  had  previously  undergone  treatment  by  amal- 
gamation or  other  metallurgical  process.  Such  material  was 
usually  collected  in  heaps  or  had  been  allowed  to  settle  in  pits 
or  natural  hollows;  in  either  case  it  had  been  exposed  to  atmos- 
pheric influences  frequently  for  long  periods  of  time.  Later, 
when  these  old  accumulations  had  been  largely  worked  out,  the 
process  was  adapted  for  the  immediate  treatment  of  material 
as  delivered  from  the  crushing  plant,  generally  after  plate  amal- 
gamation. Further  developments  of  the  process  are  its  appli- 
cation in  certain  cases  to  the  direct  treatment  of  ore  from  the 
mine,  without  other  extraction  process,  and  in  the  treatment  of 
special  classes  of  material,  such  as  concentrates,  and  by-products 
of  other  processes.  The  methods  adopted  in  handling  the  material 
naturally  differ  considerably  in  these  various  applications  of  the 
process.  We  shall  consider  them  in  the  above  order. 

(A)    HANDLING  OF  OLD  ACCUMULATIONS 

Effect  of  Natural  Settlement.  In  all  cases  the  crushed  ore 
consists  of  particles  differing  in  size  and  in  specific  gravity.  When 
these  are  carried  along  in  a  stream  of  water  of  diminishing  velocity, 
the  particles  tend  to  settle,  the  larger  and  heavier  particles  coming 
to  rest  first,  while  the  smaller  and  lighter  particles  are  carried 
farther.  As  a  consequence  of  this,  the  material  is  roughly  sorted 
into  a  layer  of  grains  diminishing  in  size  as  they  are  deposited 
farther  from  the  crushing  plant.  As,  however,  the  point  of  inflow 
and  the  direction  of  the  stream  is  varied  from  time  to  time,  the 
final  effect  is  the  production  of  layers  of  coarse  and  fine  material, 
superimposed  and  intermixed  in  a  most  irregular  way.  When 

159 


160  THE  CYANIDE  HANDBOOK 

any  attempt  is  made  to  treat  such  material  by  the  ordinary 
percolation  method,  difficulties  at  once  arise.  If  the  material 
be  dug  out  of  the  pits  and  dumped  indiscriminately  into  the 
leaching  vats,  the  charge  will  consist  of  masses  of  particles  of 
varying  degrees  of  fineness;  the  solution,  instead  of  flowing  uni- 
formly through  the  whole  charge,  will  form  channels  wherever 
there  is  least  resistance,  that  is,  in  those  parts  consisting  of  coarse 
particles.  The  very  fine  material  (slimes)  forms  layers  which  are 
practically  impervious  to  liquids;  when  these  slime  layers  are 
broken  up  and  dumped  into  the  vats  together  with  the  sand,  the 
lumps  of  slime  remain  practically  untreated.  If,  however,  the 
slime  lumps  have  become  partly  dry  before  charging,  they  may 
absorb  solution,  which  remains  in  them  when  the  tank  is  dis- 
charged ;  if  the  solution  so  absorbed  contains  gold  extracted  from 
other  portions,  this  may  lead  to  considerable  losses. 

Difficulties  in  Treatment  of  Unsized  Tailings.  —  Moreover,  the 
percolation  of  a  charge  consisting  of  particles  of  various  sizes  is 
always  more  difficult  than  when  the  particles  are  uniform,  even 
if  small,  because  in  the  first  case  the  interstices  of  the  larger 
particles  are  partially  filled  with  the  smaller  particles;  whereas 
in  the  latter  case  the  interstices  are  chiefly  filled  with  air  or  liquid. 
It  therefore  becomes  desirable  to  separate,  at  least  roughly, 
those  portions  which  can  readily  be  treated  by  percolation  from 
those  which  cannot  be  so  treated.  It  is  generally  impossible, 
in  digging  the  material  from  the  dumps  or  pits,  to  separate  the 
sandy  and  slimy  portions  sufficiently,  as  the  slime  occurs  usually 
in  thin  layers  intermixed  with  layers  of  sand,  but  one  of  the  first 
suggestions  was  to  separate  the  slime-lumps  by  passing  the  whole 
of  the  tailings  over  a  coarse  screen  or  grizzly.  (Fig.  16.)  When 
the  quantity  of  slime  is  not  too  large,  it  can  in  many  cases  be 
treated  by  partially  drying  the  material  sifted  out  as  above  de- 
scribed, and  mixing  thoroughly  with  a  large  proportion  of  sand, 
sifting  again  to  break  up  any  lumps.  Experiments,  however, 
show  that  the  extraction  from  the  sands  diminishes  in  proportion 
to  the  amount  of  slime  mixed  with  them.1 

Attempts  have  sometimes  been  made  to  mix  the  sand  and 
slime  in  situ,  by  plowing  and  harrowing  the  surface  of  the  tail- 
ings in  the  dumps  or  pits,  and  allowing  them  to  dry  as  much  as 
possible  by  exposure  before  charging  into  the  vats.  The  material 

1  Julian  and  Smart,  loc.  cit.,  p.  60. 


MECHANICAL  HANDLING   OF  MATERIAL 


161 


FIG.  16. 

is  then  passed  through  a  screen  or  disintegrator  to  obtain  a  uni- 
form mixture  for  treatment.  (Figs.  17  and  18.) 

The  Callow  Screen  (Fig.  18)  consists  of  a  perforated  endless 
traveling  belt  of  wire  cloth,  mounted  on  revolving  rollers.  The 
ore  and  water  are  fed  on  from  above.  The  belt  travels  continu- 
ously at  25  to  125  feet  per  minute.  The  coarsest  and  largest  par- 
ticles strike  the  screen  ahead  of  the  smaller  ones,  thus  leaving  a 
free  space  for  the  passage  of  particles  small  enough  to  go  through 
the  meshes  of  the  belt.  The  undersize  is  discharged  into  a  hopper 
beneath  the  upper  surface  of  the  traveling  belt. 

In  treating  old  accumulations  much  trouble  is  sometimes 
caused  by  the  presence  of  masses  of  vegetable  matter,  such  as 
grass-roots,  etc.,  derived  from  the  surfaces  on  which  the  tailings 
were  originally  deposited;  such  foreign  matter,  especially  if  par- 
tially decomposed,  causes  serious  difficulty  in  the  treatment, 


162 


THE  CYANIDE  HANDBOOK 


MECHANICAL  HANDLING   OF  MATERIAL 


163 


not  only  by  preventing  uniform  percolation,  but  by  introducing 
organic  compounds  into  the  solution,  which  act  as  powerful 
deoxidizing  agents,  and  may  even  cause  local  precipitation  of 
gold  in  the  tanks.  Whenever  possible,  such  impurities  should 
be  carefully  screened  out.  Another  source  of  trouble  is  the 
partial  oxidation  by  the  influence  of  air  and  moisture  of  iron 
pyrites  and  other  sulphides  contained  in  the  tailings,  giving  rise 


FIG.  18.  —  Callow  Screen,  supplied  by  Fraser  &  Chalmers. 

to  compounds,  soluble  in  water  or  cyanide  solution,  which  attack 
and  destroy  considerable  quantities  of  cyanide.  This  matter 
will  be  more  fully  considered  in  a  later  section  of  this  work;  it  may 
here  be  mentioned  that  this  difficulty  is  partially  overcome  by 
preliminary  water-washing  and  alkali  treatment,  applied  to  the 
tailings  before  running  on  the  cyanide  solution. 

Methods  of  Transfer.  In  general,  the  tailings  are  transferred 
from  dumps  or  pits  to  the  treatment  tanks  by  means  of  metal 
trucks  or  cars  running  on  rails,  which  are  adjusted  from  time  to 
time  to  bring  them  into  the  most  convenient  position  for  loading. 
The  cars  are  drawn  by  mules  or  pushed  by  native  laborers,  accord- 
ing to  local  conditions.  Where  circumstances  allow,  this  work 
may  be  carried  out  much  more  economically  and  conveniently 
by  mechanical  haulage,  using  conveyor  belts,  bucket  elevators, 
or  similar  devices.  (Fig.  19.)  The  rails  are  generally  carried 
over  the  top  of  the  treatment  tanks,  and  the  loaded  cars  are 


164 


THE  CYANIDE  HANDBOOK 


FIG.  19.  —  Bucket  Conveyor,  furnished  by  Hadfield' 
Steel  Foundry  Co.,  Sheffield,  Eng. 


MECHANICAL  HANDLING   OF  MATERIAL  165 

tipped  so  as  to  discharge  their  contents  on  to  a  wooden  framework 
or  grizzly,  to  assist  in  breaking  up  any  lumps  and  to  secure  a 
uniform  product  for  treatment.  When  the  tank  is  filled,  the 
surface  is  leveled  off  and  raked  over  before  applying  the  first 
wash. 

(B)    HANDLING  OF  CURRENT  MILL-PRODUCT 

If  the  tailings  leaving  a  battery  be  allowed  to  run  direct  into 
filter  tanks,  it  is  found  in  most  cases,  after  the  superfluous  water 
has  been  allowed  to  drain  off  or  has  been  decanted  from  the 
settled  sand,  that  the  material  so  collected  is  quite  untreatable 
by  cyanide,  owing  to  its  mechanical  condition :  a  partial  separation 
of  grains,  according  to  size,  takes  place  in  the  tank  as  in  the  tail- 
ings dams,  and  the  result  is  a  dense,  almost  impervious,  mass.  If 
an  attempt  be  made  to  treat  this,  the  solution  will  either  not 
percolate  at  all,  or  will  only  pass  through  the  coarser  material 
deposited  near  the  inlet. 

Settling  Pits.  —  The  first  suggestion  for  overcoming  this  diffi- 
culty was  to  construct  comparatively  small  dams  or  pits  which 
would  collect  sufficient  clean  sand  for  one  or  more  tank  charges, 
and  allow  the  water  and  the  bulk  of  the  slime  to  run  to  waste. 
The  sand  so  collected  was  then  dug  out  and  transferred  to  the 
treatment  tanks,  the  stream  of  battery  pulp  being  meanwhile 
diverted  to  another  pit.  The  outlet  of  the  collecting  pit  was 
provided  with  a  "slat  gate"  consisting  of  two  upright  grooved 
posts,  boards  being  placed  in  the  grooves  so  as  to  raise  the  hight 
of  the  overflow  -from  time  to  time  during  the  filling  of  the  pit. 
These  pits  were  frequently  lined  with  masonry  and  the  sides 
inclined  toward  the  center.  The  objections  to  this  method, 
which  is  still  used  in  many  places,  are  that  much  fine  sand  escapes 
along  with  the  slime  and  water  at  the  exit  end  (or,  on  the  other 
hand,  if  the  pit  is  made  very  large,  the  tailings  which  settle  near 
the  exit  end  are  too.  slimy  to  be  successfully  treated  by  percola- 
tion), and  the  transfer  of  the  collected  sand  from  the  pits  to  the 
treatment  tanks  is  an  operation  which  would  be  eliminated  by 
a  successful  method  of  direct  filling. 

Direct  Filling  by  Means  of  Hose.  —  As  the  chief  difficulty  in 
the  percolation  of  a  charge  of  tailings  which  is  allowed  to  run  direct 
into  the  leaching  tank  arises  from  the  uneven  distribution  of 
particles  of  different  sizes,  it  was  suggested  that  this  trouble 


166  THE  CYANIDE   HANDBOOK 

might  be  overcome  by  passing  the  stream  of  battery  pulp  through 
a  hose,  which  could  be  moved  by  hand  to  different  parts  of  the 
tank  as  the  filling  proceeded.  This  system  was  introduced  on 
the  Rand  by  Hennen  Jennings  about  1894.  The  tanks  were 
provided  with  adjustable  slat  gates,  over  which  the  slime  and 
water  passed  to  the  exit  pipe  or  launder.  This  method  is  still 
in  extensive  use,  but  it  requires  a  good  deal  of  supervision,  as, 
if  the  hose  be  not  constantly  moved  from  place  to  place,  there  will 
be  local  deposits  of  coarse  sand  and  slime  and  consequent  bad 
percolation.  In  some  more  recent  applications  of  this  system, 
the  slat  gates  are  replaced  by  canvas  blinds,  which  are  unrolled 
upward  as  the  filling  proceeds. 

Intermediate  Collecting  Tanks.  —  A  third  method,  introduced 
about  the  same  time  as  the  above  described  hose-filling  system, 
was  applied  by  Charles  Butters,  and  consists  in  the  use  of  special 
tanks  for  collecting  the  material  to  be  treated.  These  tanks  are 
filled  with  water  before  use,  and  when  the  battery  pulp  is  turned 
into  them,  the  slime  and  water  overflow  at  the  edges  into  a  cir- 
cular peripheral  launder,  whence  they  are  carried  away  for  storage 
or  further  treatment.  When  a  sufficient  quantity  of  leachable 
sand  has  collected,  this  is  transferred,  through  discharge  doors 
in  the  bottom  of  the  collecting  tank,  either  direct  into  leaching 
tanks  placed  beneath,  or  into  trucks  by  which  it  is  conveyed  to 
the  leaching  tanks.  Belt  conveyors  may  be  advantageously  used 
for  this  purpose.  The  collecting  tanks  are  provided  with  filter 
bottoms  to  assist  in  draining  off  superfluous  water.  In  order  to 
secure  uniform  mixture  and  distribution  of  the  material,  the  bat- 
tery pulp  entering  the  collecting  tank  usually  passes  through  an 
automatic  distributor,  designed  by  Charles  Butters  and  Captain 
Mein.  This  consists  of  a  conical  bowl  mounted  on  a  pillar  placed 
at  the  center  of  the  tank,  and  provided  with  radial  arms,  consist- 
ing of  tubes  of  different  lengths  bent  at  the  exit  end;  the  flow 
of  liquid  and  the  reaction  of  water  leaving  the  bent  pipes  causes 
the  apparatus  to  revolve,  and  so  produces  a  uniform  distribution 
of  the  pulp.  (Fig.  20.) 

Double  Treatment.  —  In  some  cases  the  product  collected  in 
this  way  in  the  collecting  tanks  is  sufficiently  leachable  for  direct 
cyanide  treatment,  but  in  most  cases  it  is  found  advantageous, 
after  adding  sufficient  cyanide  solution  in  the  collecting  tank  to 
saturate  the  charge,  to  transfer  the  latter  for  further  treatment 


MECHANICAL   HANDLING   OF  MATERIAL  167 

to  another  tank.  This  method  of  double  treatment  has  the  ad- 
vantage of  exposing  the  material  while  saturated  with  cyanide 
to  the  action  of  atmospheric  oxygen,  under  conditions  favorable 
for  solution  of  the  gold.  Occasionally  charges  are  transferred 


FIG.  20.  —  Revolving  Sand  Distributor  for  feeding  tailings  pulp  from  battery 
into  collecting  tanks.  With  conical  hopper,  revolving  arms  and  mouth- 
pieces, ball  bearings,  spindle  and  flanged  pillar.  [From  photograph 
furnished  by  the  Cyanide  Plant  Supply  Co.] 

a  second  or  third  time  from  one  tank  to  another  during  the  course 
of  treatment.     (See  Part  IV.,  Section  I.)     (Figs.  21  and  28.) 

(C)    TRANSFER  OF  MATERIAL  TO  HIGHER  LEVELS 

As  the  ore  and  tailings  undergoing  treatment  have  to  pass 
through  a  number  of  machines  and  appliances,  it  is  obviously 
an  advantage,  from  the  point  of  view  of  economy,  that  this  trans- 
fer should  take  place  as  much  as  possible  automatically.  Gravity 
is  utilized  by  placing  each  successive  apparatus  at  a  lower  level 
than  the  preceding  one.  It  frequently  happens,  however,  that 
the  conformation  of  the  site  on  which  the  works  are  erected  does 
not  allow  of  sufficient  fall  for  every  transfer  to  take  place  by 
gravity,  and  in  this  case  means  must  be  found  to  raise  the 
material  mechanically  to  a  higher  level. 

Conveyors,  both  of  the  belt  and  bucket  type,  are  often  used 
to  convey  ore  from  the  bins  to  the  crushers  (see  Fig.  22);  and 
also  for  transferring  tailings  from  dams  or  settling  pits  to  treat- 
ment tanks,  for  transferring  from  one  tank  to  another,  for  trans- 
porting residues  to  the  dump,  etc. 

Tailings  wheels  (see  Fig.  23)  are  very  commonly  adopted  where 
wet  material,  such  as  battery  pulp  or  the  coarse  discharge  from 
hydraulic  separators,  has  to  be  raised  to  a  higher  level.  These 


168 


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MECHANICAL   HANDLING   OF  MATERIAL 


169 


are  steel  structures,  similar  in  general  construction  to  a  bicycle 
wheel,  of  a  diameter  depending  on  the  vertical  night  to  which 
the  material  must  be  raised  —  say  20  to  70  ft.  The  rim  is  fur- 
nished with  a  frame  divided  into  compartments  or  buckets,  gen- 
erally on  the  inside,  the  walls  of  which  are  inclined  all  in  one 


FIG.  22.  —  Ore  Conveyor  (belt  system)  as  supplied  by  Fraser  and  Chalmers, 
transporting  rock  from  ore  bins  to  crushers. 

direction,  so  that  liquid  or  pulp  may  be  fed  into  them  at  the  bottom 
from  a  wooden  trough  or  launder  and  discharged  into  another 
launder  situated  just  below  the  top  of  the  wheel.  The  speed  is 
generally  from  3  to  5  r.p.m.1 

Sand  and  Tailings  Pumps.  —  In  some  cases  tailings  are  ele- 
vated by  means  of  ordinary  plunger  pumps,  running  at  a  high 
speed,  and  with  special  contrivances  to  prevent  the  settling  of 
sand  in  any  part  of  the  pump  or  delivery  pipe.  The  Frenier 

1  For  further  details,  see  Julian  and  Smart,  loc.  cit.,  p.  352. 


170 


THE  CYANIDE   HANDBOOK 


Spiral  Sand  Pump  1  is  a  well-known  apparatus  for  this  purpose. 
It  consists  of  a  spiral  tube  which  is  caused  to  revolve  so  that  at 
each  turn  the  open  end  scoops  up  some  of  the  tailings  from  the 
launder,  in  which  it  dips.  As  the  spiral  is  only  partially  immersed, 
it  takes  up  air  during  part  of  its  revolution.  On  reaching  the  center 
of  the  spiral,  the  pulp  is  discharged  into  a  delivery  pipe,  to  which 
the  spiral  is  connected  by  means  of  a  detachable  tube  and  stuffing- 


FIG.  23.  —  Tailings  Wheel,  Sons  ofGwalia  Mine.     [Furnished  by  the 
Cyanide  Plant  Supply  Co.] 

box;  through  this  delivery  tube  air  and  pulp  are  forced  by  the 
hydrostatic  pressure  of  the  liquid  in  the  spiral.  The  speed  is 
about  20  r.p.m.,  and  as  the  construction  is  very  simple  and  the 
cost  for  power  comparatively  small,  the  apparatus  presents 
considerable  advantages  over  the  centrifugal  pump.  The  lift 
is  from  14  to  24  ft.  On  the  other  hand,  it  requires  considerable 
care,  both  in  erection  and  operation,  particularly  in  starting  and 
stopping. 

(D)  PREPARATION  OF  ORE  FOR  DIRECT  CYANIDE  TREATMENT 

In  some  cases  it  has  been  found  advantageous  to  treat  the  ore 
by  cyanide  without  previous  amalgamation.     When  this  system 

1  Julian  and  Smart,  loc.  cit.,  p.  362. 


MECHANICAL  HANDLING   OF  MATERIAL  171 

is  adopted  the  ore  is  usually  crushed  dry  by  means  of  rock-breakers, 
rolls,  ball  mills,  etc.,  as  previously  described  (Sections  I  and  II). 
With  exceptionally  porous  ores,  such  as  that  of  the  Mercur  mine, 
Utah,  the  material  may  be  successfully  treated  after  merely 
reducing  to  about  \  in.  size  by  rock-breakers,  and  charging  direct 
into  the  treatment  tanks.  A  similar  method  was  adopted  at 
the  George  and  May  mine,  near  Johannesburg.  Frequently  it  is 
necessary  partially  to  dry  the  ore,  so  as  to  reduce  the  percentage 
of  moisture  below  2  per  cent.,  before  it  can  be  successfully  handled 
by  dry-crushing  machinery. 

In  the  case  of  refractory  ores,  containing  large  amounts  of 
base  metal  sulphides,  arsenic,  tellurium,  etc.,  it  is  generally  neces- 
sary to  roast  before  cyanide  treatment,  this  operation  being 
carried  out  either  by  hand,  in  reverberatory  furnaces,  or  mechani- 
cally in  one  or  other  of  the  numerous  types  of  revolving  furnace, 
or  in  furnaces  provided  with  mechanical  stirrers.  A  description 
of  some  of  the  principal  types  of  furnace  used  for  this  purpose 
will  be  found  in  Rose's  "Metallurgy  of  Gold"  (4th  ed.,  pp.  246- 
262). 

Belt  conveyors  or  similar  devices  are  frequently  used  for  trans- 
ferring the  crushed  ore  from  the  rolls  or  ball  mills  to  the  roasting 
furnaces,  and  from  the  latter  to  the  treatment  tanks.  Special 
appliances  are  also  used  for  cooling  the  roasted  ore;  thus  it  may 
be  passed  through  a  revolving  drum  containing  tubes  of  cold 
water,  or  the  conveyor  itself  may  be  water-jacketed. 

In  roasting  for  cyanide  treatment  it  may  be  observed  that  a 
partial  roast  is -sometimes  worse  than  none  at  all,  as  it  may  con- 
vert comparatively  harmless  sulphides,  etc.,  into  soluble  oxi- 
dized salts,  such  as  base  metal  sulphates,  which  act  as  rapid  and 
powerful  cyanicides.  In  general  it  may  be  said  that  where  roast- 
ing is  adopted  at  all,  a  dead  roast  is  essential.  Many  ores  formerly 
treated  by  roasting  have  been  found  to  be  amenable  to  direct 
cyanide  treatment  in  the  raw  condition,  if  finely  enough  ground. 
In  some  cases,  however,  the  effect  of  roasting  is  to  render  the 
ore  more  porous,  so  that  heavily  mineralized  ore,  which  could 
only  be  treated  raw  after  very  fine  grinding,  may  be  roasted 
after  comparatively  coarse  crushing  and  treated  direct.  The 
subject  of  roasting  for  cyanide  treatment  will  be  more  fully  dis- 
cussed in  a  later  section.  (Part  VI,  Section  III.) 


SECTION   IV 

HYDRAULIC    CLASSIFICATION,    SEPARATION,    AND 
SETTLEMENT  OF   SLIMES 

(A)    HYDRAULIC  CLASSIFICATION  BY  MEANS  OF  POINTED  BOXES 

IT  has  already  been  pointed  out  in  Section  III  that  it  is  desir- 
able to  separate  the  finer  from  the  coarser  portions  of  the  crushed 
ore  prior  to  cyanide  treatment,  as  a  different  procedure  is  neces- 
sary for  each  in  order  to  get  the  best  results.  This  mechanical 
separation  can  be  more  effectively  and  cheaply  carried  out  in 
water  than  by  any  other  means.  Various  devices  have  been  used 
from  time  to  time  with  this  object,  such  as  flat  shaking  screens 
or  jigs,  revolving  screens  or  trommels,  etc.;  but  the  simplest  and 
most  effective  for  the  present  purpose  is  the  pyramidal  box  with 
pointed  bottom,  introduced  in  its  original  form  by  Rittinger, 
about  the  middle  of  the  last  century. 

These  boxes  are  of  two  principal  types:  those  which  merely 
have  an  outlet  for  the  coarse  material  at  the  bottom  being  known 
as  Spitzkasten,  while  those  which  have,  in  addition  to  this  outlet, 
a  supply  of  water  introduced  near  the  bottom  so  as  to  cause  an 
ascending  current  are  distinguished  as  Spitzlutten.  When  a 
stream  of  water  carrying  particles  of  ore  of  different  sizes  and 
specific  gravities  is  allowed  to  flow  in  at  one  side  of  such  a  box 
and  out  at  the  opposite  side,  the  question  whether  a  given  par- 
ticle will  sink  to  the  bottom  and  be  discharged  through  the  out- 
let, or  whether  it  will  be  carried  away  by  the  overflow  at  the  top, 
depends,  (1)  on  the  area  exposed  at  right  angles  to  the  direction 
of  flow;  (2)  on  the  specific  gravity  of  the  particle;  (3)  on  the 
velocity  of  the  stream  carrying  the  particle  through  the  box;  (4) 
on  the  velocities  of  any  opposing  currents  which  it  may  meet  with. 

In  very  shallow  water,  the  velocity  of  a  falling  particle  varies 

/          ft  \ 
approximately  as  g  M  —  —  J,  where 

g  =  acceleration  due  to  gravity; 
5   =  density  of  water; 
D  =  density  of  particle. 
172 


HYDRAULIC  CLASSIFICATION  173 

In  sufficiently  deep  still  water,  the  velocity  is  uniform  and  varies 
as  a  (D  —  8),  where  a2  =  area  of  section  of  particle  at  right  angles 
to  line  of  fall. 

When  the  particle  falls  in  opposition  to  a  vertical  ascending 
current,  the  pressure  opposing  its  fall  varies  as  /  v2,  where 

/  =  area  of  surface  opposed  at  right  angles  to  current ; 
v  =  velocity  of  ascending  current. 

It  is  evident,  therefore,  that  these  machines  are  not  concen- 
trators in  the  strict  sense  of  the  term,  since  a  large  particle  of 
a  light  mineral  and  a  small  particle  of  a  heavy  mineral  might  fall 
at  the  same  rate  and  be  discharged  together.  The  mathematical 
questions  involved  in  the  construction  of  these  boxes  cannot  be 
discussed  here. 

A  full  discussion  of  the  theory  of  bodies  falling  in  water  will 
be  found  in  Rittinger's  "Lehrbuch  der  Auf bereitungskunde  " ;  an 
abstract  of  his  results  is  given  by  Julian  and  Smart,  "Cyaniding 
Gold  and  Silver  Ores"  (2d  ed.,  pp.,  369-375).  See  also  Rose, 
"Metallurgy  of  Gold"  (4th  ed.,  p.  176).  It  should  be  noted 
that  the  shape  of  the  particles  influences  their  rate  of  fall,  bodies 
presenting  a  pointed  (wedge-shaped  or  conical)  surface  to  the 
opposing  current  falling  faster  than  bodies  of  the  same  weight 
and  volume  presenting  a  flat  surface. 

In  a  case  where  the  material  treated  consists  entirely  of  fairly 
large  particles  of  the  same  specific  gravity,  the  hydraulic  separa- 
tion will  take  place  between  fine  and  coarse  particles,  that  is, 
the  material  will  be  classified  according  to  size.  In  a  case  where 
the  particles  are  approximately  of  the  same  size  but  of  different 
specific  gravities,  the  separation  takes  place  according  to  density, 
and  the  apparatus  becomes  a  true  concentrator.  A  large  spitz- 
kasten  or  spitzlutte  with  a  relatively  small  orifice  will  yield,  with 
ordinary  material  consisting  of  particles  varying  both  in  size 
and  specific  gravity,  a  product  consisting  of  approximately  equal 
falling  grains,  that  is,  grains  which  fall  at  an  equal  rate  in  still 
water. 

The  use  of  hydraulic  separators  in  cyanide  practice  is  twofold. 
In  the  first  place,  it  is  desirable  to  collect  for  separate  treatment 
the  very  coarse  portion  of  the  crushed*  ore  together  with  a  large 
proportion  of  the  heavy  mineral;  this  is  done  usually  by  passing 
the  pulp  through  a  small  spitzlutte  having  a  fairly  strong  up- 


174  THE   CYANIDE   HANDBOOK 

current.  In  the  second  place,  the  very  fine  (unleachable)  part 
of  the  ore,  generally  described  as  slime,  has  to  be  separated  from 
the  leachable  sandy  portion.  In  this  operation  the  conditions 
governing  the  separation  are  totally  different  from  those  concerned 
in  the  separation  of  coarse  particles.  Gravity  has  little  influence 
on  the  result,  and  other  factors  —  the  viscosity  of  the  pulp, 
surface  tension  and  electrostatic  repulsion  —  come  into  play. 
For  the  separation  of  slime  from  fine  sand  a  much  larger  spitzlutte 
with  a  relatively  slow  ascending  current  must  be  used. 

Details  of  the  construction  of  pointed  boxes  are  given  in  many 
works  on  metallurgy.1  We  shall  here  draw  attention  only  to  a 
few  points  of  special  interest  in  cyanide  work. 

In  order  to  prevent  the  settling  of  sand  near  the  top  of  the 
apparatus,  where  the  ascending  current  is  least  effective,  it  is 
customary  to  make  the  upper  part  of  the  box  with  vertical  sides, 
the  lower  part  being  made  either  pyramidal,  with  four  triangular 
faces  meeting  at  the  outlet,  or  in  the  form  of  a  triangular  prism, 
with  inclined  rectangular  sides  in  the  direction  of  flow  and  tri- 
angular vertical  sides  joining  these. 

In  order  to  prevent  surface  currents  from  carrying  the  pulp 
direct  to  the  overflow,  a  board  is  placed  across  the  stream  near 
the  inlet  end,  either  vertical  or  inclined,  so  as  to  force  the  stream 
of  pulp  downward  toward  the  outlet  and  bring  it  in  contact  with 
the  ascending  current  of  clear  water.  According  to  Julian  and 
Smart  (loc.  cit.,  p.  375),  "for  a  good  separation  it  is  necessary  that 
the  rising  stream  should  have,  as  nearly  as  possible,  the  same 
velocity  at  every  part  of  its  cross-section.  This  desideratum  is 
attained  by  passing  it  through  a  rectangular  passage,  one  of 
whose  dimensions  is  very  small  relatively  to  the  other."  This 
is  attained  in  some  forms  of  spitzlutte  by  making  the  whole 
apparatus  in  the  form  of  a  triangular  prism,  with  a  smaller  prism 
of  similar  shape  forming  the  partition,  so  as  to  leave  a  V-shaped 
passage,  rectangular  in  cross-section,  between  the  two.  An  ad- 
justable form  of  spitzlutte  has  also  been  introduced,  in  which 
the  inner  V  can  be  raised  or  lowered  to  vary  the  width  of  the 
passage  and  so  regulate  the  nature  of  the  product  obtained.  The 
clear  water  is  introduced  by  means  of  a  two-way  pipe  at  the  bot- 
tom of  the  apparatus;  the  continuation  of  the  pipe  forming  the 

1  See  diagrams  given  by  Julian  and  Smart  (loc,  cit.,  Figs.  172  to  176,  pp. 
375-379). 


HYDRAULIC  CLASSIFICATION  175 

outlet  is  bent  upward  and  provided  with  a  flexible  hose,  so  that 
the  level  of  outflow  can  be  varied  as  required.  The  inclination  of 
the  pointed  bottoms  should  be  not  less  than  55°  with  the  hori- 
zontal, otherwise  sand  may  collect  at  the  angles,  eventually 
falling  and  blocking  the  outlets. 

The  diameter  of  the  discharge  opening  required  is  propor- 
tional to  the  square  root  of  the  depth;  the  minimum  size  neces- 
sary to  prevent  choking  is  about  f  in.  diameter.  The  pressure 
of  the  ascending  clear  water  current  in  spitzlutten  must  be  rather 
greater  than  that  of  the  descending  pulp  stream  in  order  to  ensure 
a  clear  outflow.  By  raising  the  level  of  outflow  as  above  described, 
a  back  pressure  is  set  up,  which  enables  a  product  free  from  slime 
to  be  obtained  without  excessive  waste  of  clear  water.  When  a 
number  of  pointed  boxes  are  used  in  series  so  as  to  obtain  a  set 
of  products  of  varying  fineness,  each  successive  box  must  be 
made  wider  than  the  last,  the  width  of  each  box  being  from  1J 
to  2  times  greater  than  the  preceding  one.  For  the  first  box, 
from  4  to  6  ft.  of  width  (according  to  different  authorities)  should 
be  allowed  for  each  cubic  foot  of  pulp  flowing  per  second  through 
the  box.  The  length  of  the  successive  boxes  should  also  be 
increased,  though  this  is  a  matter  of  less  consequence.  Where 
large  quantities  are  handled,  the  stream  of  pulp  is  sometimes 
divided  between  a  number  of  boxes  placed  in  parallel,  so  as  to 
avoid  the  necessity  of  constructing  very  deep  boxes. 

Cone  Classifiers.  —  A  form  of  hydraulic  separator  which  offers 
some  advantages  over  the  ordinary  spitzkasten  and  spitzlutten 
consists  of  a  hollow  inverted  cone  of  wood  or  sheet  iron  having 
an  outlet  at  the  apex.  The  pulp  is  fed  in  either  by  means  of  a 
distributor  with  revolving  arms  which  dip  just  below  the  sur- 
face of  the  water  with  which  the  cone  is  filled,  or  through  a  cen- 
trally placed  vertical  pipe  which  descends  some  distance  beneath 
the  surface.  The  slimes  overflow  into  a  peripheral  launder  at 
the  circumference  of  the  cone.  The  underflow  may  be  made  to 
pass  to  a  second  cone,  or  a  number  of  cones  arranged  in  series 
for  more  complete  removal  of  slimes.  The  apparatus  may  be 
arranged  either  as  spitzkasten,  without  fresh  water  supply  at 
outlet,  or  as  spitzlutte  with  ascending  current  introduced  at  the 
bottom  (apex)  of  the  cone.  It  is  essential  to  have  the  apparatus 
quite  level,  so  that  a  uniform  overflow  takes  place  in  all  direc- 
tions. The  cones  have  an  angle  of  about  55°.  Owing  to  the 


176  THE  CYANIDE  HANDBOOK 

even  and  regular  flow,  a  very  perfect  separation  can  be  attained 
by  proper  adjustments.     (See  Fig.  24.) 


FIG.  24.  —  Callow  Settling  and  Pulp-thickening  Tank,  furnished  by 
the  Utah  Mining  and  Machinery  Co.,  Salt  Lake  City,  Utah. 
This  is  a  form  of  cone  classifier  which  may  be  adapted  to  serve 
either  as  spitzkasten  or  spitzlutte. 

(B)  SEPARATION  AND  SETTLEMENT  OF  SLIMES 

When  the  ore  is  very  finely  divided,  in  the  condition  generally 
described  as  slime,  frequently  it  will  riot  settle  in  any  ordinary 
time,  and  artificial  means  must  be  employed  to  remove  the  super- 
fluous water.  Filtration,  except  under  pressure,  is  not  usually 
successful,  and  may  often  be  too  costly  for  practical  use.  Since 
the  gold  values  in  such  suspended  material  are  generally  very 
easily  dissolved  in  cyanide,  it  might  be  supposed  that  settlement 
and  separation  of  the  mineral  matter  could  be  dispensed  with. 
Usually,  however,  it  is  very  difficult  to  recover  the  dissolved  gold 
in  a  concentrated  form  suitable  for  smelting,  unless  the  suspended 
ore  particles  are  removed,  although  from  time  to  time  attempts 
have  been  made  to  dissolve  and  precipitate  in  one  vessel,  as  for 
example  in  the  Pelatan-Clerici  process.  It  is  generally  simpler 


HYDRAULIC  CLASSIFICATION  177 

to  collect  the  slimy  material,  after  causing  it  to  settle  in  a  more 
or  less  concentrated  form,  by  the  addition  of  some  coagulating 
agent.  The  substance  universally  used  for  this  purpose  is  lime, 
one  part  of  which  is  said  to  be  capable  of  clarifying  between 
6000  and  7000  parts  of  water  containing  clay  in  suspension. 

There  are  other  substances  which  are  equally  or  even  more 
effective  in  causing  settlement,  but  their  use  is  precluded  either 
by  their  cost  or  on  account  of  some  chemical  property  which 
interferes  with  the  proper  working  of  the  process  by  precipitating 
the  precious  metals  or  by  setting  up  other  injurious  reactions 
with  the  ore  or  solution.  Among  substances  having  a  coagulating 
effect  on  suspended  mineral  matter  may  be  mentioned  many 
salts  of  calcium,  magnesium,  iron,  and  aluminium,  notably  the 
alums,  and,  in  a  lesser  degree,  neutral  salts  of  the  alkali  metals, 
such  as  sodium  chloride  and  various  mineral  acids.  The  follow- 
ing figures  are  taken  from  a  table  given  by  Julian  and  Smart 
(loc.  cit.,  p.  220),  representing  the  results  of  their  experiments 
on  the  relative  coagulating  effect  of  certain  salts: 

Weights  Required  to 
Produce  Equal  Co- 
agulating Effect. 

Aluminium  sulphate 100 

Potash  alum 143 

Lime  654 

Magnesia  748 

Calcium  chloride  1095 

"  carbonate 1215 

sulphate  2870 

Magnesium  sulphate 3460 

Sodium  chloride 45900 

"        sulphate     61700 

It  is  thus  seen  that,  weight  for  weight,  alum  has  about  five  times 
the  coagulating  power  of  lime. 

Application  of  Lime  in  Preparatory  Treatment  of  Slimes.  —  In 
modern  practice  a  certain  amount  of  lime  is  usually  added  in 
the  battery,  sufficient  to  dissolve  any  grease  from  the  crushing 
machinery  which  might  find  its  way  onto  the  plates.  This  has 
the  further  effect  of  coagulating  the  slime  and  thus  bringing  it 
into  more  intimate  contact  with  the  amalgamated  surface.  Hence 
it  has  been  observed  that  where  lime  is  used  in  the  battery,  the 
extraction  by  amalgamation  is  higher,  and  the  assay  value  of  the 
slimy  portion  of  the  tailings  is  lower,  than  when  the  same  ore 
is  crushed  without  addition  of  lime.  As  a  rule,  also,  a  further 


178  THE  CYANIDE   HANDBOOK 

quantity  of  lime  is  added  to  the  pulp  in  the  launder  carrying 
away  the  overflow  from  the  collecting  tanks  or  spitzlutten  used 
in  the  separation  of  the  sand.  (See  Sections  III  and  IV,  A.) 

An  ingenious  device  has  been  introduced  by  P.  S.  Tavener,1 
by  which  lime  is  fed  automatically  at  a  regular  rate  into  this 
launder.  The  overflow  carrying  the  slimy  portion  of  the  pulp 
is  led  into  a  large  spitzkasten,  in  which  the  coagulated  slime 
settles  in  practically  still  water.  If  sufficient  lime  has  been 
added,  the  overflow  from  this  spitzkasten  is  clear  enough  to  be 
used  at  once  in  the  mill,  and  is  pumped  back  for  that  purpose, 
while  the  underflow,  that  is,  the  discharge  from  the  outlet  at 
the  bottom,  consists  of  slime  carrying  perhaps  fifteen  times  its 
weight  of  water.  This  material  is  led  into  a  collecting-tank 
having  a  conical  bottom,  where  further  settlement  takes  place. 
By  using  a  sufficiently  deep  tank  for  this  purpose,  Ihe  settled 
slime  finally  obtained  may  contain  not  more  than  40  per  cent,  of 
moisture.  The  overflow  from  the  collecting  tanks  also  consists 
of  clear  water  which  can  be  returned  to  the  mill. 

1  For  details  see  Julian  and  Smart,  loc.  cit.,  p.  222. 


SECTION   V 
AMALGAMATION   AND   CONCENTRATION 

(A)  AMALGAMATION  IN  RELATION  TO  CYANIDE  TREATMENT 

A  CONSIDERATION  of  concentration,  properly  so  called,  might 
naturally  follow  the  discussion  of  hydraulic  classification,  but 
as  in  practice  some  process  of  amalgamation  almost  invariably 
precedes  concentration,  these  operations  will  be  considered  in  the 
same  .order.  In  its  earlier  applications,  the  cyanide  process 
has  been  looked  upon  merely  as  an  adjunct  to  amalgamation. 
It  has  been  applied  simply  as  a  means  of  recovering  some  part 
of  the  gold  which  is  lost  in  the  older  process,  or  which  could  only 
be  obtained  by  amalgamation  with  much  trouble  and  expense. 
This  view  still  very  largely  prevails,  and  probably  governs  the 
design  of  metallurgical  plants  at  the  majority  of  mines  in  most 
parts  of  the  world.  As  a  consequence,  while  much  care  is  taken 
to  secure  the  maximum  recovery  on  the  plates,  little  consideration 
is  given  to  the  question  whether  the  product  leaving  the  plates 
is  in  a  suitable  condition  for  yielding  the  best  extraction  by 
cyanide  treatment.  The  two  processes  are  looked  upon  as  more 
or  less  antagonistic,  and  are  usually  under  separate  managements, 
between  which  there  is  often  considerable  rivalry.  In  a  few 
localities,  notably  in  the  Rand,  it  has  been  recognized  that  the 
metallurgy  of  the  ore  should  be  regarded  as  a  single  problem, 
and  that  method  or  combination  of  methods  adopted  which  is 
found  by  experience  to  yield  the  maximum  profit.  Thus,  in 
some  instances  it  has  proved  more  advantageous  to  aim  at  a 
lower  extraction  by  amalgamation,  as  this  may  allow  of  an  in- 
creased tonnage  crushed  per  month,  the  subsequent  cyanide 
treatment  being  relied  on  to  recover  values  which  otherwise 
might  have  been  saved  in  the  mill.  Generally  speaking,  how- 
ever, it  may  be  said  that  it  is  cheaper  to  recover  gold  by  mercury 
than  by  cyanide,  especially  when  the  gold  is  in  fairly  coarse 

179 


180  THE  CYANIDE   HANDBOOK 

particles,  and  it  is  therefore  good  policy  to  make  the  amalgama- 
tion as  efficient  as  possible,  consistently  with  leaving  the  tailings 
in  such  a  condition  that  the  values  not  recoverable  by  amalgama- 
tion may  be  readily  extracted  by  cyanide.  Fortunately,  the 
conditions  which  promote  good  amalgamation  are  in  general  also 
beneficial  to  cyanide  treatment,  as,  for  example:  (1)  sufficiently 
fine  crushing  of  the  ore  (already  referred  to  in  describing  the  action 
of  stamps:  Section  I,  B);  (2)  a  slight  alkalinity  of  the  water  in 
which  the  pulp  is  suspended,  obtained  by  the  addition  of  lime 
in  the  battery;  (3)  absence  of  soluble  and  easily  decomposed 
compounds  of  the  base  metals,  which  stain  or  "  sicken  "  the  mer- 
cury and  also  act  as  cyanicides;  (4)  absence  of  oil,  grease,  and 
similar  matter. 

Amalgamation  is  carried  out  in  one  of  the  two  following  ways: 
(1)  by  causing  the  crushed  ore,  suspended  in  water,  to  come  in 
contact  with  surfaces  coated  with  a  layer  of  mercury  (plate 
amalgamation);  (2)  by  grinding  ore  and  mercury  together  in  an 
iron  pan,  with  sufficient  water  to  form  a  paste,  other  chemicals 
being  added  if  necessary  (pan  amalgamation).  Other  modi- 
fications of  less  importance  need  not  be  considered  here. 

In  the  case  of  ores  in  which  the  value  consists  principally  of 
gold,  plate  amalgamation  is  almost  universally  used;  when  the 
material  to  be  treated  is  essentially  a  silver  ore,  pan  amalgama- 
tion is  more  usual. 

In  plate  amalgamation  sheets  of  copper  coated  with  mercury 
are  placed  inside  the  mortar-box,  generally  both  on  the  feed  and 
discharge  sides,  attached  either  to  the  mortar-box  itself  or  to 
wooden  blocks.  Amalgamated  plates  are  also  placed  on  a  sloping 
table  immediately  in  front  of  the  screens,  so  that  the  pulp  flows 
over  them  as  it  leaves  the  mill.  The  practice  of  amalgamation 
inside  the  mortar-box  is  open  to  much  criticism,  on  the  ground 
of  difficulties  in  regulating  the  work,  losses  of  mercury  involved, 
etc.,  and  has  been  entirely  abandoned  in  many  places.  It  is, 
however,  defended  by  some  metallurgists  (see  Rose,  "  Metallurgy 
of  Gold,"  pp.  149,  150).  It  is  probable  also  that  the  practice  of 
placing  the  outside  plates  close  to  the  screens  may  be  largely 
abandoned  in  the  near  future,  as  it  seems  desirable  for  various 
reasons  that  the  amalgamation  should  be  conducted  in  a  room 
or  building  entirely  separate  from  the  crushing  machinery.  The 
plates  used  for  amalgamation  consist  of  pure  copper,  of  copper 


AMALGAMATION  AND  CONCENTRATION  181 

previously  coated  by  electroplating  with  a  thin  film  of  silver,  or 
of  Muntz  metal,  an  alloy  of  copper  and  zinc.  They  are  from  TV 
to  f  in.  in  thickness,  thicker  plates  being  required  for  inside  than 
for  outside  amalgamation.  For  the  latter,  the  plates  are  laid  on 
an  inclined  wooden  table,  usually  4  or  5  ft.  wide  and  12  to  14  ft. 
long,  having  raised  edges  to  retain  the  pulp. 

It  is  found  that  plates  previously  amalgamated  with  gold  or 
silver. are  more  effective  in  catching  the  precious  metals  than 
copper  plates  amalgamated  only  with  pure  mercury;  hence  the 
use  of  silvered  plates  alluded  to  above. 

Effective  amalgamation  depends  chiefly  on  keeping  the  sur- 
face of  the  plate  as  clean  as  possible,  and  in  so  regulating  the 
amount  of  mercury  that  it  forms  a  pasty  amalgam  with  the  gold 
and  silver  which  it  extracts  from  the  ore;  when  too  little  mercury 
is  added,  the  amalgam  becomes  hard  and  ceases  to  take  up  fresh 
quantities  of  the  precious  metals;  when  too  much  is  used,  it  runs 
off  in  drops  and  is  carried  away  with  the  tailings,  together  with 
any  gold  and  silver  which  it  may  have  absorbed.  Other  impor- 
tant points  are:  (1)  the  due  regulation  of  the  water-supply  so 
that  the  pulp  passing  over  the  plates  may  be  neither  too  thick 
nor  too  thin;  (2)  proper  inclination  of  the  table,  so  that  the 
pulp  comes  into  effective  contact  with  the  amalgamated  surface 
without  allowing  a  deposit  of  sand  or  mineral  to  settle  permanently 
on  it.  This  inclination  is  from  1  to  2J  in.  per  foot,  according  to 
the  nature  of  the  ore,  a  steeper  grade  being  naturally  required 
when  .  much  heavy  material  is  present.  At  intervals  during 
the  day  each  battery  of  five  stamps  is  stopped  and  the  plates 
connected  with  it  cleaned.  A  part  of  the  amalgam  is  removed 
at  the  same  time  by  means  of  a  rubber  scraper  and  fresh  mer- 
cury applied.  In  many  mills  a  certain  quantity  of  mercury 
is  also  fed  at  intervals  into  the  mortar-boxes.  The  total  amount 
of  mercury  used  varies,  of  course,  according  to  the  nature  and 
richness  of  the  ore  treated,  but  may  be  put  at  about  1  to  2  oz. 
per  ounce  of  gold  amalgamated.  Most  of  this  is  recovered  in  re- 
torting the  amalgam,  but  there  are  some  losses  which  must  now 
be  considered,  as  they  are  of  importance  in  connection  with 
cyanide  treatment. 

The  practice  of  feeding  mercury  into  the  mortar-boxes  causes 
some  of  it  to  be  broken  up,  by  the  action  of  the  stamps  and  the 
agitation  to  which  it  is  subjected,  into  very  small  globules  known 


182  THE  CYANIDE  HANDBOOK 

as  "  floured  mercury."  This  passes  through  the  screens  and  may 
be  carried  off  the  tables  by  the  stream  of  pulp,  ultimately  finding 
its  way  into  the  cyanide  vats.  If  ordinary  base  metals,  such  as 
copper,  zinc,  lead,  or  tin,  be  present  as  impurities  in  the  mercury 
used  for  amalgamation,  or  occur  in  the  ore  in  the  form  of  easily 
decomposable  compounds,  these  metals  give  rise  to  films  which 
coat  the  surface  of  the  mercury  and  entirely  prevent  amalgama- 
tion. When  this  occurs  the  mercury  is  said  to  be  "sickened." 
These  films  consist  of  the  oxides,  sulphides,  sulphates,  carbonates, 
or  other  compounds  of  the  base  metal.  In  some  cases  actual 
alloys  of  mercury  with  another  metal  may  be  formed,  and  occa- 
sionally sulphates  or  other  salts  of  mercury.1  Lead  forms  an 
amalgam  which  separates  as  a  frothy  scum,  carrying  with  it 
any  gold  which  may  be  present;  this  easily  becomes  detached 
from  the  surface  of  the  mercury  and  is  then  carried  away  by  the 
pulp.  Arsenic  and  antimony  are  particularly  harmful.  Arsenic, 
whether  in  the  metallic  state,  as  sulphide  (As2S3),  or  as  mis- 
pickel  (FeAsS),  produces  a  black  coating  which  is  a  mixture  of 
metallic  arsenic  and  finely  divided  mercury,  no  amalgam  being 
formed.  Antimony  separates  from  its  compounds  rapidly  in  a 
similar  manner,  but  the  metal  forms  an  actual  amalgam,  and 
another  part  of  the  mercury  is  converted  into  sulphide.  Bismuth 
has  a  similar  but  less  rapid  action.  All  these  compounds  readily 
break  up  into  small  particles,  so  that  sickened  mercury  is  very 
liable  to  be  carried  away  by  the  stream  of  ore  and  water  and 
hence  to  find  its  way  into  the  cyanide  plant,  giving  rise  to  various 
undesirable  reactions. 

All  metallic  sulphides  except  clean,  coarse,  undecomposed  iron 
and  copper  pyrites  have  some  action  on  mercury.  Gold  in  iron 
pyrites  largely  escapes  amalgamation,  unless  the  mineral  be 
very  finely  crushed  and  treated  in  pans,  in  which  case  much 
sickening  and  loss  of  mercury  takes  place.  The  difficulty  of 
amalgamating  gold  in  pyrites  appears  to  be  due  to  the  fact  that 
the  metal  occurs  in  thin  layers  or  plates  on  the  surfaces  of  the 
crystals  of  pyrites,  or  occupies  fissures  in  it,  the  gold  itself  being 
possibly  coated  by  thin  films  of  the  mineral  or  of  sulphur,  so  that 
contact  with  mercury  is  prevented.  Certain  gangue  minerals 
may  also  cause  losses  of  mercury;  among  these  may  be  mentioned 
heavy  spar  (barium  sulphate),  talc,  steatite,  and  similar  greasy 

1  Rose,  loc.  cit.,  pp.  133,  143,  144. 


AMALGAMATION  AND    CONCENTRATION  183 

hydrated  silicates  of  magnesia  and  alumina.  The  latter  cause 
frothing  and  form  a  coating  on  the  gold  which  prevents  amalgama- 
tion. Occasionally,  the  gold  itself,  although  apparently  free,  is 
coated  with  a  thin  film,  consisting  of  sulphur,  oxide  of  iron,  silica, 
arsenic,  metallic  sulphides,  etc.,  which  prevents  contact  with 
the  mercury  surface.  Such  gold  is  said  to  be  "  rusty,"  and  is  not 
recoverable  by  amalgamation  unless  means  be  taken  to  remove 
the  film.' 

When  the  ore  or  the  water  used  in  the  battery  contain  any 
base  metal  compound  or  any  acid  capable  of  acting  on  copper, 
yellow,  brown  or  green  stains  are  observed  on  the  surface  of  the 
plates,  which  interfere  with  amalgamation,  and  if  not  removed, 
will  increase  until  all  contact  between  the  gold  and  mercury  is 
prevented.  These  consist  usually  of  carbonates,  oxides,  and 
sulphides  of  copper,  and  perhaps  in  some  cases  of  mercurial 
compounds. 

From  the  present  point  of  view,  the  matters  of  chief  interest 
are  those  practices  which  affect  the  subsequent  cyanide  treat- 
ment of  the  tailings,  and  some  reference  must  therefore  be  made 
to  the  chemicals  used  to  promote  amalgamation.  It  has  already 
been  mentioned  that  lime  is  frequently  added  to  the  ore  in  the 
mortar-boxes,  or  to  the  battery  water.  This  neutralizes  any 
acid  substances,  such  as  soluble  salts  of  iron,  which  may  be  pres- 
ent, and  which  might  tarnish  the  plates,  and  also  helps  to  dis- 
solve any  oily  matter  introduced  into  the  ore  or  feed  water  from 
the  grease  used  in  lubricating  the  crushing  machinery.  Any 
kind  of  grease  ha*s  a  very  deleterious  effect  on  amalgamation. 
The  addition  of  lime,  moreover,  causes  flocculation  and  settle- 
ment of  the  fine  suspended  ore  particles,  thus  bringing  them  in 
contact  with  the  amalgamated  surfaces.  This  treatment  renders 
the  material  more  suitable  for  cyaniding,  both  from  a  mechanical 
and  from  a  chemical  point  of  view,  but  in  certain  cases  it  may 
render  the  amalgamation  so  effective  that  the  values  remaining 
in  the  tailings  are  reduced  below  the  point  at  which  cyanide 
treatment  is  profitable.  (See  Jourri.  Chem.,  Met.  and  Min.  Soc. 
of  South  Africa,  II,  87.)  (Proc.  2,  657.) 

In  order  to  remove  the  stains  on  the  plates  to  which  reference 
is  made  above,  and  to  produce  a  bright  clean  surface  for  amalgama- 
tion, certain  chemicals  are  used,  the  chief  being  sal  ammoniac 
and  cyanide.  Both  of  these  are  solvents  of  the  copper  com- 


184  THE  CYANIDE  HANDBOOK 

pounds  which  cause  the  discoloration.  When  they  are  to  be 
applied,  the  battery  is  stopped  and  the  spots  scrubbed  with  the 
required  solution.  The  chemical  is  then  washed  off,  and  gen- 
erally a  fresh  quantity  of  mercury  is  added  before  allowing  the 
pulp  again  to  flow  over  the  plate.  It  is  obvious  that  the  use  of 
cyanide  for  this  purpose  is  open  to  very  serious  objections.  It 
is  applied  in  the  form  of  a  fairly  strong  solution,  perhaps  0.5 
per  cent.  KCy,  and  even  though  the  mill  is  stopped  during  the 
dressing  of  the  plates,  some  part  of  the  solution  used  must  almost 
inevitably  find  its  way  into  the  launder  which  conveys  the 
tailings  from  the  mill,  where  it  will  dissolve  some  gold.  Unless 
the  whole  of  the  battery  water  is  returned  to  the  mill,  a  part  of 
these  dissolved  values  will  be  lost.  If  used  at  all,  the  plates  should 
be  carefully  washed  with  fresh  water  immediately  after  the 
cyanide  has  been  applied,  and  such  water  should  be  run  into  a 
separate  receiver.1  The  practice  of  adding  cyanide  in  the  mortar- 
boxes  is,  of  course,  still  more  objectionable,  and  could  only  be 
defended  where  complete  arrangements  are  made  for  crushing 
with  cyanide  solution,  which  involves  passing  all  the  liquid  used 
in  the  mill  through  the  precipitation  boxes.  Where  no  lime  is 
used  in  the  battery  and  the  water  contains  acid  iron  salts,  these 
would  probably  destroy  in  most  cases  any  excess  of  cyanide 
used  in  cleaning  the  plates  before  any  appreciable  amount  of 
gold  had  been  dissolved  from  the  tailings. 

Cyanide  is  also  to  some  extent  a  solvent  of  oily  and  fatty 
matters,  but  probably  only  by  virtue  of  any  free  alkali  it  may 
contain.  For  this  purpose  a  solution  of  caustic  soda  or  of  sodium 
carbonate  is  much  more  effective;  and  as  already  mentioned, 
lime  acts  beneficially  in  this  way. 

Clean  floured  mercury  may  be  collected  and  recovered  by 
agitation  with  a  large  mass  of  fresh  mercury,  especially  if  a  little 
alkali  be  added  to  dissolve  any  film  of  grease  which  may  be  present. 
The  sickening  of  mercury  may  often  be  remedied  by  the  addition 
of  sodium  amalgam,  which  contains  2  to  3  per  cent,  of  metallic 
sodium.  The  action  of  this  substance  is  to  reduce  the  metallic 
oxides,  forming  caustic  soda,  which  at  once  dissolves  in  the  water 
and  is  incidentally  beneficial  as  a  solvent  of  grease  and  some  other 
impurities.  The  base  metal  is  liberated  in  the  metallic  form  and 

1  See  paper  by  A.  von  Gernet,  "  Losses  of  Gold  in  Mill  Water,"  in  "  Proc.  Chem., 
Met.  and  Min.  Soc.  of  South  Africa,"  II,  529. 


AMALGAMATION  AND  CONCENTRATION  185 

usually  amalgamates  with  the  mercury.  In  the  case  of  antimony, 
however,  the  sulphide  of  mercury  present  in  the  film  is  attacked, 
forming  sodium  sulphide,  which  acts  upon  a  further  quantity  of 
the  antimonial  mineral,  forming  more  antimony  amalgam  and 
liberating  sulphureted  hydrogen,  so  that  in  this  case  the  use  of 
sodium  amalgam  probably  does  more  harm  than  good. 

Hydrochloric,  or  still  better,  nitric  acid,  will  dissolve  some 
of  the  impurities  in  sickened  mercury;  the  latter  readily  dissolves 
some  of  the  mercury  itself,  exposing  a  bright  metallic  surface, 
so  that  the  particles  will  coalesce  on  agitation.  Nitrate  of  mer- 
cury also  removes  the  stains  on  the  plates,  forming  metallic 
mercury  and  copper  nitrate. 

The  foreign  substances  introduced  during  the  crushing  and 
amalgamating  processes,  and  which  may  influence  the  results  of 
subsequent  cyanide  treatment,  may  be  here  enumerated: 

(1)  Metallic  mercury,  due  to  the  use  of  excessive  quantities 
in  dressing  the  plates,  or  to  flouring  or  sickening,  as  described 
above. 

(2)  Gold  and  silver  amalgam,  scoured  off  the  plates  by  coarse 
particles  of  ore. 

(3)  Base  metals,  originally  present  in  the  mercury  and  ulti- 
mately  converted  into   oxides  or   alloys,   coating  the   sickened 
mercury. 

(4)  Lime,  in  solution  in  the  water  carrying  the  pulp  from 
the  battery. 

(5)  Oil  and  grease  from  the  bearings  of  machinery,  from  feed 
water,  or  from  rmine  candles. 

(6)  Fragments  of  metallic  iron  from  the  shoes,  dies,  and  other 
parts  of  the  crushing  machinery. 

(7)  Particles  of  brass  and  copper  from  plates,  screens,  and 
the  percussion  caps  used  in  blasting. 

(8)  Chips  of  wood,  rubber,  leather,  and  other  miscellaneous 
materials  which  may  accidentally  fall  into  the  stream  of  battery 
pulp. 

(B)  CONCENTRATION  IN  RELATION  TO  CYANIDE  TREATMENT 

General  Principles  of  Concentration 

Concentration  may  be  defined  as  any  process  by  which  a 
mass  of  material  is  separated  into  two  portions,  one  containing 


186  THE  CYANIDE  HANDBOOK 

a  greater  proportion  by  weight  of  the  valuable  constituents  than 
the  other.  This  separation  is  generally  carried  out  by  utilizing 
some  difference  in  the  physical  nature  of  the  particles  which 
constitute  the  mass,  with  a  consequent  difference  in  behavior 
when  subjected  to  the  same  forces.  The  methods  of  hydraulic 
separation  by  means  of  spitzkasten  and  spitzlutten  have  already 
been  discussed.  In  these  methods  the  forces  involved  are  prin- 
cipally gravity,  inertia,  resistance  to  hydrostatic  pressure,  and 
(in  the  case  of  the  finer  particles)  viscosity  and  probably  elec- 
trostatic repulsion.  Concentration  by  machines  of  this  class 
must  always  be  imperfect  from  a  metallurgical  point  of  view, 
since,  as  pointed  out  above  (Section  IV,  A),  the  product  obtained 
consists  of  particles  differing  in  size  and  specific  gravity,  small 
particles  of  heavy  material  being  collected  together  with  large 
particles  of  light  material;  whereas  an  ideally  perfect  concentrator 
would  separate  the  whole  of  whatever  mineral  or  substance  it 
was  designed  to  save,  and  the  product  yielded  by  it  would  there- 
fore consist  entirely  of  particles  having  the  same  specific  gravity. 
No  machine  actually  fulfils  this  condition.  What  is  aimed  at  in 
practice  is  the  separation  of  the  material  to  be  dealt  with  into 
two  products: 

(a)  Concentrates,  consisting  of  a  relatively  small  total  mass, 
containing  a  relatively  large  part  of  the  total  valuable  constitu- 
ents originally  present,  and  a  relatively  small  part  of  the  worth- 
less ingredients. 

(b)  Tailings,  having  a  relatively  large  total  mass  containing 
as  little  as  possible  of  the  original  valuable  contents. 

The  forces  which  are  utilized  in  the  ordinary  systems  of  con- 
centration, and  which  effect  their  purpose  owing  to  the  difference 
of  their  action  on  different  kinds  of  particles,  are:  (1)  gravity; 
(2)  inertia  and  centrifugal  force;  (3)  adhesion  between  surfaces 
of  concentrating  machine  and  the  class  of  particles  to  be  separated; 
(4)  Adhesion  between  the  fluid  used  in  the  apparatus  and  the 
particles  to  be  separated. 

When  applied  to  gold  and  silver  ores,  concentration  as  a  rule 
follows  amalgamation.  The  pulp,  or  crushed  ore  suspended  in 
water,  as  it  leaves  the  plates,  passes  to  the  concentrating  ma- 
chines, which  are  of  three  or  four  principal  types. 


AMALGAMATION  AND  CONCENTRATION  187 

Old  Types  of  Concentrator 

The  oldest  and  most  primitive  types  of  concentrator  depend 
for  their  action  solely  on  the  fact  that  in  a  flowing  stream  the 
heavier  particles  carried  by  the  water  tend  to  settle  and  collect 
against  any  obstacle  or  irregularity  in  the  bed  of  the  stream. 
This  is  the  principle  of  the  "Long  Tom"  and  other  forms  of 
riffled  'sluices,  in  which  the  material  is  washed  down  an  inclined 
trough  or  launder,  either  stationary  or  subjected  to  a  rocking 
motion,  the  coarser  particles  of  gold  and  the  heavier  minerals 
being  caught  against  strips  of  wood  (riffles)  nailed  at  intervals 
across  the  bed  of  the  launder.  Another  primitive  device  is  to 
allow  the  pulp  to  flow  over  a  sloping  table  covered  with  blankets 
or  some  kind  of  rough  cloth,  the  heavy  particles  which  settle  to 
the  bottom  of  the  stream  being  caught  and  retained  by  the  hairs 
and  interstices  of  the  cloth.  These  cloths  are  removed  at  inter- 
vals and  the  heavy  material,  known  as  "blanketings,"  which  has 
collected  on  them  is  brushed  or  washed  off,  by  hand  or  mechani- 
cally, into  any  suitable  receptacle. 

In  many  concentrators  some  device  is  used  for  keeping  the 
pulp  in  a  state  of  agitation,  so  that  the  lighter  particles  may  be 
thrown  into  suspension  and  carried  off  by  the  flowing  stream, 
while  the  heavier  particles  are  moved  only  a  short  distance  along 
the  bed  of  the  machine.  In  the  various  types  of  "buddies"  the 
pulp  flows  over  a  stationary  inclined  bed,  on  which  it  is  stirred 
by  means  of  revolving  arms  carrying  brushes  or  similar  con- 
trivances; or  the  same  effect  is  produced  by  revolving  the  inclined 
bed  and  using  stationary  brushes.  These  machines  generally 
have  a  conical  form;  in  the  convex  buddle  the  pulp  is  fed  at  the 
apex  and  the  tailings  discharged  into  a  launder  at  the  circum- 
ference; in  the  concave  buddle  the  feed  is  at  the  circumference 
and  the  tailings  flow  away  through  an  opening  in  the  center. 
The  heavy  mineral  collects  near  the  feed  and  the  lighter  particles 
are  carried  off  as  tailings;  but  in  all  such  devices  a  large  quantity 
of  ore  is  spread  out  over  the  surface  between  the  feed  and  dis- 
charge, consisting  of  a  mixture  of  different  kinds  of  particles, 
gradually  diminishing  in  richness  from  the  feed  to  the  discharge. 
To  obtain  a  satisfactory  concentration,  this  "middle  product" 
must  be  collected  from  time  to  time  and  again  fed  onto  the  ma- 
chine, necessitating  repeated  handling  of  the  same  material,  so 


188  THE  CYANIDE  HANDBOOK 

that  the  capacity  of  the  concentrator  is  very  small  in  compari- 
son with  the  labor  and  power  required  to  work  it. 

Modern  Types  of  Concentrator 

Modern  concentrating  machinery,  as  applied  to  gold  ores, 
apart  from  the  pointed  boxes  already  described,  is  almost  entirely 
of  two  types:  percussion  tables,  and  endless-belt  tables. 

(a)  Percussion  Tables.  —  In  these  machines  the  material  to 
be  concentrated  is  fed  onto  a  sloping  table  having  a  smooth  sur- 
face of  wood,  iron,  sheet  copper,  linoleum,  etc.,  together  with 
sufficient  water  to  make  a  thin  pulp,  some  device  being  often 
used  for  securing  a  uniform  distribution  and  regular  feed  of  ore 
and  water  onto  the  table.  The  ore,  thus  spread  out  in  a  thin 
layer,  is  kept  in  a  constant  state  of  agitation  by  a  series  of  blows 
delivered  against  one  end  of  the  table  by  a  set  of  cams  or  some 
similar  contrivance.  These  blows  cause  the  heavier  particles 
which  have  settled  out  of  the  flowing  pulp  to  travel  gradually 
toward  one  end  of  the  table,  where  they  are  collected  in  a  box 
or  other  receptacle;  the  lighter  particles  are  thrown  into  suspen- 
sion and  carried  off  by  the  stream  of  water,  either  to  the  oppo- 
site end  of  the  table  or  over  the  side  into  a  launder,  by  which 
they  are  discharged.  In  some  types  of  percussion  table,  the  ore 
spreads  itself  out  into  a  fan-shaped  layer  in  which  the  different 
minerals  are  sorted  according  to  their  specific  gravity;  the  heaviest 
particles  form  a  line  at  the  extreme  edge  and  may  be  collected 
separately;  then  follow  in  succession  bands  of  (say)  galena,  lead 
carbonate,  pyrites,  blende,  black  oxide  of  iron,  coarse  and  fine 
sand,  and  finally  slime.  The  middle  products,  if  necessary,  may 
be  collected  in  a  separate  launder  leading  to  an  elevator,  which 
returns  them  to  the  table  for  reconcentration. 

Among  the  older  types  of  machine  based  on  the  percussion 
principle  may  be  mentioned  the  Gilt  Edge  concentrator;  among 
modern  improved  types  are  the  Wilfley,  Woodbury,  James,  and 
many  other  concentrating  tables  of  similar  design.  Through  the 
courtesy  of  the  Wilfley  Mining  Machinery  Co.,  the  following 
brief  description  of  this  well-known  machine  is  given. 

The  latest  form  (No.  5,  1906)  of  the  Wilfley  Concentrator 
consists  of  a  flat  deck  or  table  mounted  on  rockers  and  supported 
by  cast-iron  plates  bolted  rigidly  to  a  timber  frame.  The  move- 
ment is  imparted  at  the  upper  end  of  the  table  by  means  of  a  toggle 


AMALGAMATION  AND  CONCENTRATION 


189 


operated  by  an  eccentric  shaft,  the  length  of  stroke  being  ad- 
justed by  turning  a  hand  wheel,  which  raises  and  lowers  a  wedge 
block  at  one  end  of  the  toggle,  varying  the  stroke  from  £  to  1  in. 
The  shaft  makes  about  240  r.p.m.  When  in  use  the  table  is 
set  so  as  to  be  slightly  inclined  from  the  feed  to  the  discharge 
side.  It  is  generally  constructed  of  redwood,  in  narrow  strips  laid 
diagonally  to  avoid  warping,  and  strengthened  by  steel  stringers 
extending  the  full  length  of  the  table,  to  obviate  any  bending  of 
the  table  surface.  It  is  covered  with  linoleum,  over  a  part  of 
which  are  tacked  parallel  strips  of  wood,  forming  riffles.  This 
kind  of  surface  readily  holds  the  ore  particles,  and  is  also  durable, 
impervious  to  water,  and  easily  replaced.  (See  Figs.  25  and  26.) 


FIG.  25. — Wilfley  Concentrator.     (Showing  driving  gear.  From  cut  furnished 
by  the  Wilfley  Mining  Machinery  Co.) 

The  pulp  is  fed  onto  the  table  through  holes  in  the  upper  side 
of  the  pulp-box,  placed  near  the  upper  corner  on  the  feed  side  of 
the  table.  Water  is  delivered  by  an  open,  perforated  box  extend- 
ing the  whole  length  of  the  feed  side,  below  the  pulp-box.  The 
tailings  are  discharged  over  the  edge  of  the  table  on  the  discharge 
side  (opposite  the  feed)  into  a  launder.  The  concentrates  pass 
off  at  the  lower  end  of  the  table  (opposite  the  driving  gear) .  Any 
required  portion  of  the  tailings  may  be  returned  as  middlings, 
by  a  separate  launder,  to  an  elevating  wheel  connected  with  the 
same  eccentric  shaft  which  moves  the  table,  and  passed  back 


190  THE  CYANIDE   HANDBOOK 

to  the  feed  box.  This  arrangement  prevents  losses  of  mineral 
which  might  otherwise  occur  through  irregular  feeding  of  pulp 
or  wash-water.  The  bank  of  mineral  formed  by  the  return  ele- 
vator tends  to  prevent  a  rush  of  material  toward  the  tailings 
launder.  The  finest  slimes  are  discharged  near  the  head  of  the 
table;  the  remaining  minerals  arrange  themselves  in  the  order 


FIG.  26.  —  Wilfley  Concentrator.     General   view   showing  distributing   box 
and  riffles.     [From  cut  furnished  by  the  Wilfley  Mining  Machinery  Co.] 

of  their  specific  gravity,  the  heaviest  passing  off  at  the  foot  of 
the  table.  It  is  sometimes  desirable  to  reconcentrate  the  middlings 
after  further  crushing,  on  a  separate  table,  instead  of  using  an 
elevator  as  above;  in  this  case  the  feed  to  the  table  should  be 
regular. 

(6)  Belt  Tables.  —  Belt  concentrators  usually  consist  of  an 
endless,  revolving,  rubber  belt,  flanged  at  the  edges,  which  travels 
slowly  over  a  couple  of  rollers,  placed  in  such  a  position  that  the 
upper  part  of  the  belt  forms  a  slightly  inclined  surface,  having 
an  area  of  about  12X4  feet.  At  the  same  time  a  slight  but  rapid 
shaking  motion  is  imparted  to  the  machine,  either  laterally  or 
longitudinally.  Ore  and  water  are  distributed  as  uniformly  as 
possible  across  the  width  of  the  traveling  surface,  near  its  upper 
end,  and  the  belt  is  caused  to  revolve  in  the  opposite  direction 
to  the  flow  of  the  pulp;  that  is,  it  travels  up  the  incline  while 
passing  above  the  rollers.  By  means  of  another  pair  of  rollers 
placed  beneath  the  machine,  the  belt  on  its  return  journey  is 
made  to  pass  through  a  tank  or  trough  containing  water,  which 
serves  to  collect  the  concentrates.  The  heavy  particles  of  mineral 


AMALGAMATION  AND  CONCENTRATION 


191 


fall  to  the  bottom  of  the  pulp  stream  and  cling  to  the  surface  of 
the  rubber;  as  the  belt  ascends,  it  carries  them  past  the  pulp 
distributor,  behind  which  a  perforated  pipe  delivers  a  number  of 
small  jets  of  water.  These  serve  to  clean  the  concentrates  still 
further  by  washing  away  the  lighter  particles,  while  the  heavier 
material  is  carried  past  them  and  delivered  to  the  collecting  box 
underneath.  The  light  portions  are  carried  by  the  stream  of  water 
down 'the  slope  of  the  belt  and  discharged  into  a  launder  at  the 
lower  end.  To  this  type  of  machine  belong  the  Frue  Vanner  (Fig. 
27),  the  Embrey  Concentrator,  the  Liihrig  Vanner,  etc.  The  lat- 


FIG.  27.  —  Frue    Vanner,    supplied   by   Fraser  and   Chalmers. 

ter  delivers  a  middle  product  at  the  side  of  the  belt,  and  receives 
a  series  of  blows  from  a  cam-shaft,  in  these  respects  resembling 
the  Wilfley  table.  (See  above.) 

Other  Systems  of  Concentration 

Other  types  of  concentrator  are  used  in  special  circumstances 
such  as  jigs,  shaking  screens,  dry  blowers,  centrifugal  separators, 
etc. ;  but  these  need  not  be  described  here.  Some  reference,  how- 
ever, may  be  made  to  the  recently  introduced  methods  of  "oil 
concentration"  and  "flotation,"  in  which  gravity  plays  no  part 
whatever. 

In  the  Elmore  oil  concentration  process,  the  mixture  of  crushed 
ore  and  water  is  fed  into  a  slightly  inclined  revolving  cylinder 
together  with  a  considerable  quantity  of  crude  mineral  oil.  Owing 


192  THE  CYANIDE  HANDBOOK 

to  some  physical  action  at  present  imperfectly  understood,  cer- 
tain minerals,  particularly  those  having  a  bright  "metallic" 
surface,  adhere  to  the  oil.  On  discharging  the  contents  of  the 
cylinder  into  tanks  containing  water,  the  oil  floats  to  the  top, 
carrying  with  it  the  adhering  minerals,  which  are  then  separated 
from  it  by  means  of  a  rapidly  revolving  centrifugal  extractor. 
By  this  means  gold,  galena,  copper,  and  iron  pyrites  and  other 
lustrous  minerals  may  be  separated  from  earthy  carbonates, 
sulphates,  oxides,  etc.,  and  from  sand  and  siliceous  minerals 
generally. 

The  "flotation"  process  utilizes  the  surface  tension  of  water 
as  a  means  of  separating  the  same  class  of  minerals,  namely,  those 
having  a  lustrous  surface.  The  pulp  is  distributed  by  means  of 
a  revolving  cylinder,  rifled  internally,  so  that  it  falls  at  a  certain 
angle  on  the  surface  of  water.  Those  mineral  particles  which 
under  the  circumstances  are  not  "wetted,"  float  on  the  surface 
and  are  carried  to  a  receptacle  where  they  are  caused  to  sink  by 
agitation.  The  remainder  of  the  pulp  sinks  at  once  in  the  collect- 
ing tanks  and  is  discharged  from  the  bottom. 

Concentration  Previous  to  Cyanide  Treatment 

In  the  early  days  of  the  cyanide  process  it  was  thought  that 
the  solvent  could  not  be  successfully  applied  to  material  contain- 
ing coarse  gold  or  refractory  minerals  having  considerable  chemical 
action  on  cyanide;  hence  the  system  was  generally  adopted  only 
for  tailings  after  concentration.  The  metallurgical  scheme  com- 
monly carried  out  in  dealing  with  gold  ores  was  as  follows :  Crush- 
ing by  rock-breakers  and  stamps;  amalgamation  of  coarse  gold 
in  the  battery;  concentration  of  battery  tailings,  generally  by 
means  of  Frue  Vanners  (the  object  being  to  obtain  the  maximum 
gold  value  with  the  minimum  of  other  substances) ;  cyanide  treat- 
ment of  the  tailings  from  the  concentrators  in  cases  where  the 
values  still  remaining  in  them  were  sufficient  to  pay  the  cost. 
The  concentrates  were  generally  roasted  in  reverberatory  or  other 
furnaces  and  treated  by  chlorination,  yielding  a  high  percentage 
of  extraction,  but  at  such  a  heavy  cost  that  the  operation  could 
only  be  conducted  in  large  establishments  treating  the  accumu- 
lated product  from  a  number  of  mines. 

This  system  has  gradually  been  replaced  by  the  method  of 


AMALGAMATION   AND  CONCENTRATION  193 

hydraulic  classification  described  above,  in  which  the  tailings 
after  amalgamation  undergo  only  a  rough  concentration  in  spitz- 
lutten,  the  object  being  not  to  obtain  a  close  saving  of  the  values 
by  concentration,  but  to  obtain  a  product  carrying  the  bulk  of 
the  coarser  and  heavier  mineral  particles,  so  that  this  product 
may  receive  special  treatment,  leaving  the  main  portion  of  the 
pulp  as  fine  sand  suitable  for  ordinary  treatment.  Roughly 
speaking,  the  pulp  leaving  the  battery  is  finally  obtained  in  three 
products:  (1)  a  comparatively  small  amount  of  coarse  heavy 
sand,  requiring  a  long  time  of  treatment  with  rather  strong  solu- 
tions; (2)  a  much  larger  amount  of  fine  sand,  amenable  to  cyanide 
treatment  with  weak  solutions,  not  over  0.25  per  cent.  KCN,  and 
(say),  3  to  4  days'  contact;  (3)  slime,  capable  of  treatment  with 
very  weak  solution  by  some  system  of  agitation,  followed  by 
settlement  and  decantation,  or  by  filter-pressing. 

Under  ordinary  circumstances  this  more  recent  system  is 
found  to  yield  a  greater  profit,  though  probably  a  lower  per- 
centage of  extraction  than  the  earlier  method.  It  also  has  the 
advantage  that  the  whole  of  the  gold  recovery  can  be  made  in 
a  metallurgical  plant  under  direct  control  of  the  management 
at  each  mine,  none  of  the  products  being  necessarily  sold  to 
smelters  or  reduction  works.1 

A  still  more  modern  system,  largely  adopted  in  Western 
Australia  and  coming  into  general  use  in  other  fields,  consists  in 
reducing  the  whole  of  the  ore  to  such  a  fine  state  of  division  that 
it  can  be  treated  (with  or  without  amalgamation  and  hydraulic 
classification)  by  agitation  with  cyanide  solution,  the  gold-bearing 
liquor  being  finally  separated  by  filter-pressing.  This  system  has 
only  been  rendered  possible  by  the  introduction  of  cheap  devices 
for  fine  grinding,  such  as  the  tube  mill  already  described.  (See 
Section  II,  D.) 

Cyanide  Treatment  of  Concentrates 

Where  the  heavy  mineral  consists  almost  entirely  of  clean 
unoxidized  iron  pyrites,  the  concentrates,  even  when  carrying  a 
large  percentage  of  sulphides,  can  generally  be  treated  success- 
fully by  cyanide,  but  a  long  period  of  treatment,  sometimes 
amounting  to  three  or  four  weeks,  is  necessary,  and  some  arti- 

1  See  also  Rose,  loc.  tit.,  pp.  221-222. 


194  THE  CYANIDE  HANDBOOK 

ficial  means  must  generally  be  adopted  for  securing  the  amount 
of  oxygen  needed  for  the  reaction.  The  concentrates  must  be 
turned  over  or  discharged  from  one  tank  to  another  from  time 
to  time  during  the  treatment,  and  it  is  sometimes  advantageous 
to  aerate  the  solutions.  In  special  cases  oxidizing  agents  or  other 
chemicals  may  be  added  as  an  aid  to  solution.  In  cases  where 
the  concentrates  have  become  partially  oxidized  by  exposure, 
difficulties  arise  owing  to  the  action  of  soluble  sulphates  of  iron 
and  of  insoluble  basic  sulphates  on  the  cyanide.  These  diffi- 
culties may  be  largely  overcome  by  giving  a  preliminary  treat- 
ment with  a  mineral  acid  (H2SO4,  or  HC1).1  The  reactions 
involved  are  discussed  in  the  section  of  this  work  dealing  with 
the  chemistry  of  the  process. 

The  treatment  of  spitzlutte  concentrates  presents  less  diffi- 
culty, both  because  the  percentage  of  refractory  material  is  smaller 
and  because  the  coarse  sand  renders  the  mass  readily  leachable; 
moreover,  since  the  material  is  collected  by  settlement  from  a 
large  bulk  of  water,  ail  soluble  salts  will  have  been  removed 
before  the  cyanide  is  applied,  and  partial  oxidation  of  the  pyrites 
to  basic  sulphates  is  not  likely  to  occur  unless  the  treatment  of 
the  product  be  unduly  delayed. 
1  See  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  I,  98-103,  133-134. 


PART  IV 

THE    DISSOLVING   PROCESS 

THE  extraction  of  gold  and  silver  from  a  mass  of  pulverized 
material  by  means  of  cyanide  or  other  solvent  may  be  brought 
about  in  one  of  two  ways:  (1)  By  causing  the  solution  to  pass, 
either  by  gravity  or  by  hydraulic  or  atmospheric  pressure,  through 
a  stationary  body  of  the  material  to  be  treated.  (2)  By  agitating 
solvent  and  material  together  by  suitable  appliances,  so  as  to 
bring  them  into  intimate  contact,  and  then  separating  them, 
either  by  settlement  and  decantation  or  by  filtration. 

The  term  "  percolation  "  is  used  simply  to  signify  the  passage 
of  a  liquid  through  porous  material,  whether  anything  is  dis- 
solved by  the  liquid  or  not.  The  term  "leaching"  means  the 
extraction  of  soluble  matter  from  a  mass  of  material  by  the  pas- 
sage of  a  liquid  through  it.  The  two  terms,  however,  are  often 
used  in  technical  literature  as  though  they  were  interchangeable. 
The  words  "vat"  and  "tank"  also  are  commonly  used  as  inter- 
changeable, although  some  attempts  have  been  made  to  restrict 
the  use  of  the  word  "tank"  to  vessels  holding  liquids. 


SECTION  I 

PERCOLATION 
(A)    LEACHING  VATS 

IN  modern  practice,  percolation  is  almost  invariably  carried 
out  in  circular  vats  of  wood  or  iron,  having  a  flat  bottom  on 
which  rests  a  filter-frame,  composed  of  thin  parallel  strips  of 
wood  covered  with  canvas  or  other  suitable  cloth  to  form  a  filter. 
In  the  early  days  of  the  process,  square  wooden  vats  were  com- 
monly used,  but  these  presented  many  drawbacks,  both  in  con- 
struction and  use,  and  usually  caused  heavy  losses  by  leakage. 
Cement-lined  masonry  tanks  have  also  been  used  occasionally. 
The  vats  should  rest  on  a  solid  foundation,  supported  above  the 
ground  on  masonry  piers,  so  as  to  allow  a  free  passage  under- 
neath. Wooden  vats  are  constructed  of  a  number  of  upright 
staves,  beveled  at  the  edges,  so  that  when  fitted  together  and 
tightened  by  the  hoops  they  form  a  water-tight  structure.  Each 
of  the  staves  has  a  notch  or  "check,"  a  few  inches  from  the 
bottom,  to  receive  the  floor  or  bottom  of  the  tank.  The  latter 
is  constructed  of  planks  with  tongues  and  grooves,  so  that  they 
may  be  tightly  joined,  and  is  cut  in  the  form  of  a  circle  of  the 
required  diameter,  allowing  for  the  check  in  the  staves.  The 
hoops  are  made  from  lengths  of  round  iron,  the  ends  being  tightly 
screwed  together.1  Steel  vats  are  constructed  of  plates  t\  in- 
to f  in.  in  thickness,  riveted  together.  Those  used  for  the  sides 
of  the  tanks  are  bent  to  the  required  curve  by  passing  them 
through  rolls.  The  vats  are  strengthened  by  angle-iron  rings  at 
top  and  bottom.1  When  carefully  constructed  there  is  little 
tendency  to  leak.  Small  leaks  may  be  stopped  with  fine  slime, 
paraffin  wax,  or  vaseline. 

Either  type  of  vat   has   its  advantages  and   disadvantages. 

1  For  details  of  construction  see  Julian  and  Smart,  "  Cyaniding  Gold  and 
Silver  Ores,"  2d  edition.,  Ch.  XXXIV  and  XXXV. 

197 


198 


THE  CYANIDE   HANDBOOK 


Wooden  vats  are  more  liable  to  leakage,  and  a  certain  quantity 
of  solution  containing  gold  and  silver  values  may  be  absorbed 
by  the  wood.  Iron  vats,  on  the  other  hand,  are  more  expensive, 


both  in  first  cost  and  maintenance;  leaks,  when  they  do  occur, 
are  more  difficult  to  stop,  especially  at  the  bottom  of  the  tank, 
after  the  filter  has  been  laid.  They  are  also  liable  to  distortion 


PERCOLATION  199 

under  internal  pressure  when  the  ore  in  the  vat  is  irregularly 
distributed.  This  causes  cracks  through  the  sand  charge  and 
consequently  bad  percolation,  as  the  liquid  forms  channels.  The 
latter  defect  can  be  remedied  by  using  sufficiently  heavy  material 
and  bracing  with  angle-iron.  The-  accompanying  illustration 
(Fig.  28)  shows  a  large  South  African  Plant  with  double  treat- 
ment tanks  constructed  of  steel. 

With  regard  to  the  absorption  of  solution  by  wooden  vats, 
experiments  by  F.  L.  Bosqui1  and  others  would  seem  to  show 
that  this  is'  not  a  very  serious  matter.  Somewhat  greater  absorp- 
tion appears  to  take  place  when  the  immersion  in  solution  is 
intermittent  than  when  continuous.  Thus  a  piece  of  redwood 
having  an  area  of  180  sq.  in.,  immersed  continuously  for  3  weeks 
in  a  gold  cyanide  solution,  absorbed  gold  to  the  value  of  $1.07; 
whereas  a  similar  piece  of  wood  of  the  same  area,  treated  for  the 
same  length  of  time,  but  immersed  for  16  hours  and  dried  in  the 
sun  for  8  hours  each  day,  absorbed  gold  to  the  value  of  $2.45  per 
ton  of  wood.  Tests  on  a  screen  frame  of  rough  pine,  which  had 
been  in  contact  with  solution  for  12  months,  gave,  however,  the 
following  result: 

Bottom  of  frame,  continuously  immersed:  Gold  absorbed,  $5.32 
per  ton  of  wood. 

Top  of  frame,  alternately  exposed  and  immersed,  about  half 
time  under  solution:  Gold  absorbed,  $2.87  per  ton  of  wood. 

S.  H.  Williams2  states  that  a  launder  through  which  63,000 
tons  of  auriferous  solution  carrying  0.07  per  cent,  cyanide  had 
passed  was  burned,  and  that  the  ashes  were  found  to  contain 
2.766  oz.  gold  and  32.464  oz.  silver. 

Filter-frames.  —  These  are  formed  by  a  number  of  parallel 
wooden  slats  6  to  9  in.,  apart,  above  which,  and  at  right  angles 
to  them,  are  nailed  wooden  strips  of,  say,  1  sq.  in.  section,  laid 
1  in.  apart.  Large  frames  are  made  in  sections,  and  round  holes 
are  cut  over  the  discharge  doors. 

Filter-cloths.  —  These  are  generally  of  cocoanut  matting, 
sometimes  covered  with  an  upper  cloth  of  duck  or  canvas  or, 
better,  hessian.  The  edges  of  the  cloth  are  tucked  tightly  be- 
tween the  sides  of  the  vat  and  the  filter-frame,  and  the  joint  is 
sometimes  made  water-tight  by  wedging  a  rope  into  this  space. 

i"Min.  Sc.  Press,"  April  14,  1906. 

2 "Trans.  I.  M.  M.,"  Bui.  No.  11,  Aug.  17,  1905. 


200  THE  CYANIDE   HANDBOOK 

Parallel  strips  of  wood  are  sometimes  laid  above  the  cloth  and 
at  right  angles  to  the  strips  below,  to  protect  the  cloth  during 
the  discharging  of  the  vat.  These  are  fastened  lightly,  so  as  to 
be  easily  removed. 

Discharge  Doors.  —  Some  description  of  these  is  given  below. 
Holes  for  the  doors  are  cut  in  symmetrical  positions  in  the  bottom 
of  the  tank  and  through  the  filter-frame  and  cloth,  and  are  so 
arranged  that  the  discharge  of  the  tank  can  be  carried  out  with 
the  minimum  of  labor.1 

Solution  Outlet.  —  This  is  placed  in  any  convenient  position 
below  the  filter-frame,  and  is  furnished  with  a  cock  and  a  pipe 
leading  to  the  precipitation  department. 

Dimensions  of  Vats.  —  Tanks  have  been  constructed  to  hold 
any  quantity  up  to  600  tons  of  tailings,  and  may  be  as  much  as 
60  ft.  in  diameter.  There  is  no  difficulty  in  constructing  larger 
ones  if  required.  The  depth  is  generally  considerably  less  than 
the  diameter.  Ordinary  sizes  are  20  to  30  ft.  in  diameter,  and 
8  to  14  ft.  inside  depth.  Tanks  for  storing  solution  are  commonly 
made  deeper  in  proportion  to  diameter  than  leaching  tanks,  as 
in  the  latter  the  efficiency  of  percolation  has  to  be  considered. 

(B)    THE  LEACHING  PROCESS 

Conditions  for  Effective  Percolation.  —  As  already  pointed  out, 
it  is  very  desirable  to  separate  the  slime  as  much  as  possible  from 
the  material  which  is  to  be  treated  by  percolation;  and  better 
results  are  obtained  when  the  grains  of  sand  are  more  or  less  of 
the  same  size  than  when  all  sizes  are  mixed  together.  (See  Part  III.) 
To  ensure  good  results  it  is  necessary  to  lay  the  material  uni- 
formly throughout  the  vat,  without  undue  compression,  and 
finally  to  level  the  surface  by  raking  it  over  before  introducing 
cyanide  solution.  By  this  means  the  solution  percolates  evenly 
through  all  parts  without  forming  channels.  The  tank  is  com- 
monly filled  to  within  an  inch  or  so  of  the  top,  but  the  material 
settles  considerably  when  moistened  with  solution.  The  valves 
at  the  outlet  pipes  are  closed  until  all  bubbling  (due  to  displace- 
ment of  air)  has  ceased;  this  ensures  a  better  aeration  of  the 
charge  than  if  the  valves  are  left  open  in  order  that  the  solution 
sinking  into  the  mass  may  drive  the  air  out  through  the  exit  pipe. 

1  Julian  and  Smart,  loc.  tit,,  p.  297. 


PERCOLATION  201 

In  certain  cases,  as  in  the  treatment  of  accumulated  sand 
which  has  not  undergone  hydraulic  separation,  or  where  sufficient 
lime  has  not  been  added  in  the  battery  or  elsewhere  to  neutralize 
the  latent  acidity  of  the  material,  it  is  necessary  to  add  lime  to 
the  charge  as  the  tank  is  filled.  This  is  sometimes  spread  in  a 
layer  over  the  surface  of  the  tank,  and  raked  over  before  adding 
the  first  wash  of  solution. 

Preliminary  Water-wash.  —  This  is  occasionally  given  for  the 
purpose  of  removing  soluble  cyanicides,  that  is,  substances  which 
would  consume  cyanide  during  the  treatment.  It  is  generally 
unnecessary  when  the  sands  have  been  obtained  by  hydraulic 
separation  or  have  settled  from  water  in  collecting  tanks.  When 
used  for  the  purpose  of  removing  soluble  salts  of  iron,  copper,  etc., 
it  is  best  not  to  add  lime  or  other  alkali  to  the  charge  or  to  the 
water  used  in  washing,  as  these  salts  would  be  wholly  or  partially 
precipitated  by  the  alkali. 

Alkali  Wash.  —  It  is  a  common  practice  to  give  a  preliminary 
treatment  with  an  alkaline  solution,  commonly  of  lime,  the  chief 
object  being  to  secure  the  neutralization  of  insoluble  cyanicides, 
such  as  basic  ferric  sulphate,  before  adding  the  strong  cyanide 
solution,  and  thus  avoid  any  undue  consumption  of  cyanide  in 
the  latter.  In  practice  this  amounts  to  a  treatment  with  very 
weak  cyanide  solution,  as  a  certain  amount  of  cyanide  from 
previous  charges  finds  its  way  into  the  water  used  for  the  alkali 
wash,  for  which  a  special  storage  tank  is  commonly  reserved. 
The  alkali  wash  is  pumped  on  and  allowed  to  leach  through  con- 
tinuously until  the  effluent  is  distinctly  alkaline.  The  first  por- 
tions of  liquid  passing  through  are  sometimes  run  to  waste,  but 
as  they  commonly  contain  gold,  it  is  better  to  allow  the  whole  of 
the  effluent  to  return  to  the  alkali  storage  tank  until  it  shows 
sufficient  strength  in  cyanide  for  effective  precipitation;  then  it 
is  diverted  to  the  precipitation  boxes,  the  small  quantity  of 
cyanide  thus  introduced  into  the  alkali  wash  being  no  serious 
disadvantage.  The  tank  is  allowed  to  drain  as  much  as  possible, 
so  as  to  avoid  undue  dilution  of  the  strong  solution  which  is  after- 
ward applied.  Occasionally  the  strong  solution  is  preceded  by 
a  weak  cyanide  wash,  also  with  the  object  of  diminishing  the 
dilution  which  would  otherwise  take  place  in  the  strength  of  the 
strong  solution;  but  the  more  usual  practice  is  to  add  the  latter 
as  soon  as  the  alkali  wash  has  sufficiently  drained  off,  it  being  then 


202  THE  CYANIDE   HANDBOOK 

assumed  that  latent  acidity  in  every  part  of  the  charge  has  been 
properly  neutralized. 

Strong  Solution.  —  Before  adding  the  strong  solution  the  out- 
let cock  is  closed.  The  solution  is  then  pumped  on  to  the  vat 
from  the  strong  solution  storage  tank,  in  which  it  has  previously 
been  made  up  to  the  required  strength  in  cyanide,  usually  by 
adding  the  calculated  amount  of  liquor  from  the  "dissolving 
tank/'  a  small  vat  placed  above  the  storage  tanks  and  used  for 
dissolving  the  solid  cyanide  from  the  cases.  In  some  plants  the 
cyanide  is  dissolved  directly  over  the  leaching  tanks,  by  placing 
the  solid  lumps  in  a  perforated  box  into  which  weak  solution  from 
the  storage  tanks  is  pumped.  This  method  is  not  to  be  recom- 
mended, as  it  must  lead  to  the  treatment  of  some  parts  of  the 
charge  with  unnecessarily  strong  solution  and  consequent  waste 
of  cyanide.  The  solution  is  pumped  on  until  the  charge  remains 
well  covered  with  liquid  to  a  depth  of  two  or  three  inches.  It  is 
then  allowed  to  stand,  frequently  for  twenty-four  hours  or  longer, 
so  as  to  allow  the  charge  to  soak  thoroughly  in  strong  solution.  It 
is  a  better  plan,  however,  to  draw  off  the  solution  as  soon  as  all 
bubbling  has  ceased,  say  after  one  or  two  hours,  and  allow  it  to 
run  off  until  the  effluent  shows  a  sufficient  strength  in  cyanide 
for  effective  dissolution  of  the  values;  the  outlet  valve  is  then 
closed  and  more  strong  solution  is  pumped  on,  until  the  charge 
is  again  covered  to  the  required  depth.  The  charge  is  now  left 
standing  under  strong  solution  as  long  as  may  be  considered 
necessary.  The  object  of  this  procedure  is  to  ensure  the  satura- 
tion of  the  whole  charge  with  solution  of  sufficient  strength,  since 
but  little  diffusion  takes  place  in  the  leaching  tank,  one  solution  dis- 
placing another  without  mingling  with  it  to  any  considerable  extent. 

The  strength  of  solution  to  be  used  depends  on  the  nature  of 
the  material  to  be  treated.  Roughly  speaking,  the  richer  it  is 
in  gold,  the  stronger  will  be  the  cyanide  solution  required,  but 
this  rule  is  by  no  means  universal.  Where  silver  is  to  be  ex- 
tracted, much  stronger  solutions  are  commonly  required  than  for 
gold  alone,  partly  owing  to  the  greater  weight  of  metal  which 
has  to  be  dissolved  and  partly  to  the  presence  of  accompanying 
minerals  which  consume  much  cyanide.  This  matter  is  discussed 
in  the  sections  dealing  with  the  chemistry  of  the  process.  Under 
normal  conditions  a  strength  of  0.25  per  cent.  KCN  *  (=0.1  per 

1  5  Ib.  potassium  cyanide  or  3.8  Ib.  sodium  cyanide  per  ton  of  solution. 


PERCOLATION  203 

cent.  CN)  is  a  good  standard  to  work  with,  though  in  the  case  of 
clean  tailings  free  from  coarse  gold,  a  strength  of  0.1  per  cent. 
KCN  (=  0.04  per  cent.  CN)  is  often  sufficient  to  give  a  good 
extraction  of  the  values.  (See  pp.  105-107.)  When  the  charge  has 
stood  long  enough  under  strong  solution,  the  outlet  cock  is  opened 
and  the  liquid  allowed  to  drain  off  to  the  precipitation  boxes;  the 
effluent  is  tested  for  cyanide  and  also  for  alkali  to  ensure  that 
it  is  in  good  condition  for  precipitation.  This  will  generally 
be  the  case  if  the  preliminary  alkali  wash  has  been  properly 
carried  out.  For  the  treatment  of  silver  ores  and  concentrates, 
strengths  of  0.3  per  cent,  to  0.5  per  cent.  KCN  (6  to  10  Ib.  per 
ton)  are  commonly  used,  and  in  some  cases  as  high  as  1  per  cent. 

Weak  Solution.  —  When  the  strong  solution  has  sufficiently 
drained  off,  weak  solution  is  pumped  on  from  the  storage  tanks. 
It  is  often  desirable  to  allow  the  charge  to  remain  exposed  to 
the  air  for  some  time  before  pumping  on  weak  solution,  and 
occasionally  the  surface  is  raked  over,  so  as  to  allow  access  of 
oxygen  to  the  material,  to  enable  the  weak  solution  to  dissolve 
any  gold  not  extracted  by  the  strong  solution.  The  liquor  used 
for  weak  solution  is  commonly  that  which  passes  from  the  pre- 
cipitation boxes,  used  again  without  further  addition  of  cyanide; 
but  it  may  in  some  cases  be  necessary  to  bring  up  its  strength, 
say  to  0.15  per  cent.  KCN  (=  0.06  per  cent.  CN,  i.e.,  3  Ib.  KCN  or 
2J  Ib.  NaCN  per  ton  of  solution),  by  adding  the  required  amount 
of  stock  solution  from  the  dissolving  tank. 

The  weak  solution  is  generally  added  in  a  number  of  succes- 
sive washes,  gradually  diminishing  in  strength  to  say  0.05  per 
cent.  KCN  ( —  0.02  per  cent.  CN) ;  these  are  either  drawn  off  im- 
mediately or  left  in  contact  only  a  short  time,  a  fresh  wash  being 
added  as  soon  as  the  previous  one  has  sunk  well  below  the  sur- 
face of  the  charge.  More  effective  extraction,  however,  is  gen- 
erally obtained  by  allowing  each  wash  to  drain  as  completely  as 
possible  before  adding  the  next,  though  this  is  not  always  prac- 
ticable, owing  to  considerations  of  time.  Unless  the  sand  treated 
is  absolutely  free  from  slime,  the  rate  of  percolation  gradually 
diminishes,  in  consequence  of  the  settling  of  slime  particles  in 
the  interstices  of  the  charge  and  on  the  filter-cloth.  The  main 
object  of  the  weak  solution  treatment  is  to  displace  the  strong 
solution  and  thus  remove  from  the  charge  the  values  which  have 
already  been  dissolved. 


204  THE  CYANIDE  HANDBOOK 

The  amount  of  weak  solution  necessary  varies  greatly  accord- 
ing to  circumstances;  'the  total  volume  used  is  generally  con- 
siderably greater  than  that  of  the  strong  solution,  and  the  time 
occupied  is  also  greater.  In  some  plants  a  medium  solution  is 
used  after  the  strong  solution,  a  special  storage  tank  being  em- 
ployed for  this. 

Final  Water-wash.  —  As  the  liquid  with  which  the  charge  is 
saturated  after  the  last  weak  wash  has  been  drawn  off  still  con- 
tains gold  in  solution,  it  is  the  custom  where  practicable  to  dis- 
place this  by  addition  of  water.  It  will  be  obvious,  however, 
since  the  liquid  so  displaced  is  added  to  the  general  stock  of  solu- 
tion in  the  plant,  that  the  amount  of  water  which  can  be  used  in 
this  way  is  very  limited.  The  amount  of  solution  in  stock  is  a 
fixed  quantity,  depending  upon  the  .  storage  accommodation. 
The  amount  of  final  water-wash,  therefore,  cannot  exceed  the 
difference  between  the  moisture  originally  present  in  the  charge 
and  that  in  the  tailings  as  discharged,  except  in  cases  where  a 
part  of  the  solution  is  run  to  waste  or  where  losses  occur  by  evapo- 
ration. In  practice,  the  final  wash  is  generally  given  with  the 
weakest  cyanide  solution  available. 

Quantities  of  Solution  Used  in  Percolation.  —  No  definite  rule 
can  be  given  as  to  the  quantities  of  each  class  of  solution  that 
should  be  used,  nor  as  to  the  time  occupied  by  each  in  contact 
and  leaching.  These  considerations  depend  partly  on  the  arrange- 
ment of  the  plant  and  partly  on  the  nature  of  the  material  treated. 
In  an  ordinary  case,  about  1J  tons  of  liquid  will  pass  through 
the  vat  for  every  ton  of  sand  (dry  weight)  which  it  contains; 
say  J  ton  of  strong  solution,  1  ton  of  weak  solution,  and  |  ton  of 
alkali  wash  and  final  water-wash.  It  is  convenient  to  have  the 
size  of  the  tanks  such  that  one  tank  will  contain  the  whole  amount 
of  sand  produced  per  day.  Thus,  with  a  plant  consisting  of  seven 
leaching  tanks,  one  might  be  filled  and  one  discharged  every  day, 
allowing  five  days  for  the  actual  cyanide  treatment  —  two  days 
for  strong  solution  and  three  for  weak.  Some  such  arrangement 
as  this  greatly  simplifies  the  routine  of  operations  in  the  plant. 

Upward  Percolation.  —  In  the  case  of  material  containing 
slime,  which  is  apt  to  settle  on  the  filter-cloth  and  impede  filtra- 
tion, one  or  more  of  the  solutions  may  be  introduced  from  below 
and  forced  upward  through  the  charge  by  hydraulic  pressure. 
When  this  is  done  slowly  and  carefully,  the  formation  of  channels 


PERCOLATION 


205 


is  avoided  and  the  filter-cloth  kept  free  from  slime.  After  the 
charge  has  stood  covered  with  solution  for  a  sufficient  time,  the 
liquid  is  again  drawn  off  from  below,  and  subsequent  washes 
generally  added  from  above  and  allowed  to  percolate  downward. 

(C)    DOUBLE  TREATMENT 

The  system  of  intermediate  filling  has  already  been  described 
(Part  III,  Section  III),  and  it  has  been  noted  that  the  collecting 
vats  are  sometimes  used  as  preliminary  treatment  vats.  Usually, 
the  final  treatment  vats  are  placed  immediately  beneath  the 
collecting  vats,  so  that  the  material  may  be  readily  transferred 
from  one  to  the  other  by  bottom  discharge  doors.  The  general 
method  is  to  give  the  alkali  wash,  if  any,  and  at  least  a  part  of 
the  strong  solution,  treatment  in  the  upper  vat,  so  that  when  the 
transfer  takes  place  the  material  saturated  with  strong  solution 
is  freely  exposed  to  the  air.  The  remainder  of  the  strong  solution 
treatment  and  the  final  washing  with  weak  solution  and  water 
takes  place  in  the  lower  vat.  In  some  cases,  especially  in  the 
treatment  of  concentrates,  it  is  found  advantageous  to  transfer 
the  charge  a  second  or  third  time. 

The  following  scheme  of  treatment,  based  on  a  method  pro- 
posed by  W.  R.  Feldtmann  for  treatment  of  tailings  at  the 
Luipaards  Vlei  Estate/  will  illustrate  the  method: 

FIRST  TREATMENT:  CHARGE,  165-170  TONS  TAILINGS 


Tons  Solution 
put  on 

Strength:  KCy 

Time  Leaching: 
Hours 

Remarks 

Strong  .  .  . 
Medium  .  . 

27 

27 

0.25  per  cent 
0,20    "       " 

66  to  70 

Drained  off 
without 

Weak  .... 

27 

0.15    "       " 

standing 

Extraction  by  first  treatment,  67  per  cent. 
SECOND  TREATMENT 


Tons  Solution 
put  on 

Strength:  KCy 

Time  Leaching: 
Hours 

Remarks 

Medium  .  . 
Weak  .... 
Water 

20  to  25 
75 
20  to  30 

0.20            percent. 
0.15  to  0.10  "     " 

179 

In    successive 
washes 

F.  White,  "  Trans.  I.  M.  M.,"  VII,  124  (1899). 


206 


THE  CYANIDE   HANDBOOK 


It  is  stated  that  in  some  cases  a  difference  of  over  20  per  cent, 
in  the  extraction  has  been  obtained  through  the  introduction  of 
double  treatment.  The  method  is  extensively  adopted  in  the 
treatment  of  pyritic  ores,  and  in  cases  where  refractory  minerals 
are  present,  as  in  most  silver  ores.  (See  below.) 

(D)    DISCHARGING  OF  TREATED  MATERIAL  (RESIDUES) 

Where  facilities  exist  for  the  purpose,  the  treated  sand  may 
be  rapidly  and  economically  discharged  by  sluicing,  using  a  strong 
jet  of  water.  This  method  is  frequently  adopted  for  discharging 
treated  slimes.  (See  below.)  When  the  first  cyanide  plants  were 
erected  in  South  Africa,  the  only  method  of  discharging  the  vats 
was  by  shoveling  over  the  side  into  trucks,  this  procedure  invol- 
ving great  waste  of  labor,  even  with  the  shallow  square  tanks 
then  in  use.  In  1891  the  system  of  "bottom  discharge"  was 
introduced  by  Charles  Butters,  whereby  the  cost  of  discharging 
was  reduced  to  about  a  quarter  of  that  for  the  previous  system. 
Tanks  have  also  been  constructed  with  doors  in  the  side  for  dis- 
charging, but  since  it  is  evident  that  the  material  to  be  discharged 
must  be  thrown  a  greater  average  distance  when  the  door  is  at 
the  side  than  when  at  the  bottom,  the  bottom  doors  have  been 
almost  universally  adopted. 

The  type  of  discharge  door  first  designed  by  Butters  and  still 
in  general  use  consists  essentially  of  a  circular  steel  or  cast-iron 


FIG.  29.  —  James  Patent  Discharge  Door  as  furnished  by  the  Cyanide 
Plant  Supply  Co. 

disk,  fitting  into  a  flanged  cast-iron  tube  which  passes  through 
the  filter-cloth,  frame,  and  bottom  of  the  tank.  These  doors 
are  9  to  16  in.  in  diameter,  and  have  a  bolt  passing  through  the 
center,  carrying  a  butterfly-nut  underneath  the  tank,  by  which 
the  door  can  be  fastened  or  unfastened  as  required.  (See  Fig.  29.) 


PERCOLATION  207 

A  more  recent  type  of  door  is  hinged  on  one  side  and  secured 
by  a  bolt  and  nut  on  the  opposite  side.  In  either  case  certain 
precautions  are  necessary  to  obtain  a  water-tight  joint.  When  a 
tank  is  to  be  filled,  the  door  is  closed  and  the  discharge  tube 
(passing  through  the  filter)  is  filled  with  sand,  with  a  covering  of 
clay  or  slime.  In  discharging,  which  is  generally  done  by  hand, 
the  door  is  first  unscrewed,  a  rod  is  pushed  upward  into  the  tank, 
and  a  hole  is  dug  down  to  the  opening.  The  material  is  then 
shoveled  through  the  latter  into  a  truck  standing  on  rails  beneath 
the  vat.  When  the  tanks  are  very  deep  an  additional  steel  tube 
is  sometimes  attached  to  the  upper  edge  of  the  discharge  tube 
before  the  tank  is  filled,  and  when  needed  other  sections  can  be 
added  above  this.  It  is  then  only  necessary  to  dig  down  to  the 
uppermost  section  before  beginning  to  discharge.  The  extra 
tubes  are  removed  in  succession  as  the  discharging  proceeds. 

In  places  where  labor  is  costly,  various  mechanical  appli- 
ances have  been  introduced  for  discharging  tanks.  One  of  these, 
the  Blaisdell  vat  excavator,  consists  of  a  number  of  revolving 
radial  arms  carrying  steel  disks  inclined  at  an  angle  with  the 
arms.  The  machine  is  placed  over  the  top  of  the  tank  to  be  dis- 
charged, and  as  it  revolves  the  material  is  pushed  by  the  disks 
toward  the  center  and  passes  through  a  discharge  door  to  trucks 
or  to  a  belt-conveyor  beneath.  A  shorter  pair  of  radial  arms,  also 
carrying  disks,  is  used  to  counteract  the  tendency  of  the  material 
to  pile  up  toward  the  center.1 

1  For  details,  see  Julian  and  Smart,  loc.  cit.,  p.  192. 


SECTION  II 

AGITATION 
(A)    AGITATION  BY  MECHANICAL  STIRRERS 

IN  the  first  plant  erected  in  South  Africa  —  the  experimental 
plant  near  the  Old  Salisbury  battery,  which  was  in  operation  in 
the  early  part  of  1890  —  a  system  of  agitation  with  paddles  was 
used,  combined  with  subsequent  filtration  of  the  pulp  by  suction. 
It  was  considered  that  a  better  contact  of  solution  and  ore,  and 
consequently  more  rapid  dissolution  of  the  gold,  would  be  ob- 
tained by  the  agitation  system.  This  view  was  no  doubt  correct, 
but  the  method  was  very  soon  abandoned  in  favor  of  percolation, 
which  required  so  much  less  expenditure  of  power  and  was  far 
simpler  in  execution.  Modern  practice,  however,  shows  a  ten- 
dency to  revert  to  agitation  methods,  and  consequently  percola- 
tion is  a  far  less  important  factor  in  cyanide  work  than  it  was  a 
few  years  ago.  Many  ores  have  been  shown  to  yield  a  much 
higher  percentage  of  their  values  when  every  portion  is  crushed 
at  least  fine  enough  to  pass  a  150-mesh  sieve  than  when  crushed 
moderately  fine,  say  to  30  or  40  mesh,  and  a  separation  made  of 
sands  and  slimes  for  different  treatment.  Ore  crushed  to  150- 
mesh  cannot,  strictly  speaking,  be  regarded  as  slime,  as  it  is 
generally  possible  to  separate  from  it  a  considerable  amount  of 
fine  sand  which  is  perfectly  leachable.  It  may,  however,  be  con- 
veniently treated  by  agitation,  and  in  many  cases  this  system 
would  be  more  profitable  than  hydraulic  separation  of  the  sands 
for  percolation. 

The  overflow  from  the  spitzliitten  or  collecting  tanks  —  in 
some  plants  the  entire  mill-product  reduced  to  a  sufficient  fine- 
ness —  generally  goes  first  to  a  large  spitzkasten,  the  overflow 
from  which,  consisting  of  practically  clear  water,  is  returned  to 
the  battery.  The  underflow  from  this,  consisting  of  thickened 
slime,  passes  either  direct  to  the  agitation  tanks  or  into  special 
collecting  tanks  with  conical  bottoms,  whence  a  further  quantity 

208 


AGITATION  .      209 

of  water  is  withdrawn.  The  moisture  in  the  pulp  withdrawn 
from  the  bottom  of  these  tanks  may  in  some  cases  be  reduced 
by  this  means  to  50  per  cent.  The  agitation  tanks  are  provided 
with  paddles  revolving  about  a  central  vertical  shaft.  The  latter 
is  supported  by  a  platform  running  across  the  centers  of  the  vats; 
at  the  upper  end  of  the  vertical  shaft  is  a  bevel-wheel,  operated 
by  a  horizontal  countershaft.  When  a  sufficient  charge  has  been 
collected,  the  agitator  is  set  in  motion,  arid  a  sample  taken  of  the 
well-mixed  pulp.  Lime  is  added,  if  necessary,  and  then  sufficient 
cyanide  solution  to  give  a  pulp  of  about  4  to  5  tons  liquid  for  every 
ton  of  dry  slime  present.  When  the  material  is  to  be  subsequently 
treated  by  filter-pressing,  a  much  thicker  pulp  than  this  is  com- 
monly used,  say  1|  to  1|  tons  liquid  per  ton  of  slime. 

The  strength  of  solution  depends  on  the  material  to  be  treated, 
but  it  is  commonly  much  less  than  that  required  for  percolation 
treatment  of  sands.  In  many  cases  a  satisfactory  percentage 
of  the  gold  may  be  dissolved  with  solutions  of  0.01  per  cent.  KCN 
(=  0.004  per  cent.  CN,  i.e.,  0.2  Ib.  KCN  or  0.15  Ib.  NaCN  per  ton 
of  solution,  or  4  to  5  times  these  amounts  per  ton  of  dry  slime). 
Slimes  from  pyritic  or  refractory  ores,  especially  if  silver  or  copper 
minerals  be  present,  may  require  much  stronger  solutions. 

The  agitation  is  continued  until  all  soluble  gold  or  silver  may 
be  assumed  to  be  dissolved.  The  time  required  for  this  also 
varies  greatly,  from  3  to  36  or  even  48  hours.  In  an  ordinary 
case,  6  hours  will  be  sufficient.  In  a  thick  pulp  the  values  gen- 
erally dissolve  more  slowly  than  in  a  thin  one,  and  the  strength 
of  solution  also  affects  the  result.  An  ordinary  strength  for  the 
treatment  of  clean  slimes  is  0.05  per  cent.  KCN  (  =  0.02  per  cent. 
CN),  but  twice  or  three  times  this  strength  may  be  needed  for 
refractory  material. 

The  agitator  is  then  stopped;  in  some  cases  the  stirring  gear 
is  so  arranged  that  the  paddles  can  be  lifted  above  the  level  to 
which  the  settled  slimes  will  reach.  The  tank  is  allowed  to  stand 
without  further  agitation  till  a  sufficiently  complete  settlement 
has  taken  place,  which  may  require  from  9  to  as  much  as  60 
hours.  As  soon  as  a  clear  liquid  shows  above  the  surface  of  the 
settling  pulp,  decantation  is  begun.  This  is  generally  carried 
out  by  means  of  a  pipe,  jointed  near  the  bottom  of  the  tank  and 
with  the  upper  end  supported  by  means  of  a  float  just  below  the 
surface  of  the  liquid.  The  exit  pipe  passes  out  near  the  bottom 


210  THE  CYANIDE  HANDBOOK 

of  the  tank.  The  pipe  is  lowered  as  the  settlement  proceeds,  so 
that  clear  solution  is  continuously  drawn  off  and  passes  on  to 
the  precipitation  plant.  When  filter-presses  or  some  form  of 
suction  filter  are  to  be  used,  the  pulp  is  transferred  direct  from 
the  agitation  tanks,  without  settlement,  by  means  of  hydraulic 
or  atmospheric  pressure,  or  by  suitable  pumps,  to  the  filtering 
apparatus.  The  apparatus  known  as  "montejus"  is  frequently 
used  for  this  purpose. 

(B)    AGITATION  BY  CIRCULATING  THE  PULP  AND  INJECTION  OF  AIR 

A  method  often  used  in  place  of,  or  in  conjunction  with, 
mechanical  stirrers  is  to  withdraw  the  pulp  continuously  from 
the  bottom  of  the  tank  and  return  it  to  the  top  by  means  of  cen- 
trifugal or  other  pumps.  This  method  has  the  advantage  of  secur- 
ing a  more  complete  mixture  of  the  particles,  especially  when  a 
little  coarse  material  is  present,  than  could  possibly  be  obtained  by 
any  form  of  paddle  agitator,  and  the  further  advantage  that 
during  the  transfer  the  pulp  is  thoroughly  exposed  to  the  air  and 
the  action  of  the  cyanide  thereby  accelerated. 

In  cases  where  further  oxidation  is  considered  necessary, 
arrangements  have  been  made  for  causing  the  pulp  as  it  returns 
to  the  agitation  tank  to  fall  from  a  hight  and  to  be  scattered  in 
the  form  of  spray.  Another  device,  due  to  H.  T.  Durant,  which 
seems  to  be  still  more  effective  in  securing  oxidation,  is  to  place  a 
small  suction  valve  on  the  intake  pipe  of  the  centrifugal  pump; 
this  draws  in  air,  in  the  form  of  minute  bubbles  intimately  mixed 
with  the  pulp,  though  of  course  with  some  loss  in  the  lifting 
power  of  the  pump. 

Sometimes  agitation  by  injection  of  compressed  air  through 
a  perforated  pipe  is  also  used.  In  this  case  the  pipe  is  bent 
around  the  bottom  of  the  vat,  so  as  to  allow  air  to  pass  through 
the  charge  at  as  many  points  as  possible.  In  carrying  out  this 
method  of  agitation,  the  best  results  are  obtained  by  using  tanks 
that  are  very  deep  in  comparison  with  their  diameter.  Tanks 
for  this  purpose  erected  at  Pachuca,  Mexico,  are  15  ft.  in  diameter 
and  45  ft.  high;1  they  are  constructed  with  a  conical  bottom, 
the  air  being  delivered  through  the  apex  of  the  cone  under  suffi- 
cient pressure  to  prevent  settling  of  the  pulp  on  the  conical  sur- 

1  M.  R.  Lamb,  "  Notes  on  Air-agitation,"  "  Eng.  and  Min.  Journ.,"  LXXXVI, 
901  (Nov.  7,  1908). 


AGITATION  211 

face.  The  pressure  required  is  from  22  to  35  Ib.  per  sq.  in.;  15  to 
20  cu.  ft.  of  air  are  used  per  charge,  which  it  is  stated  gives  a  vigor- 
ous agitation  and  excellent  extraction.  Slime,  fine  sand,  and  con- 
centrates are  treated  by  this  method.  The  apparatus  used,  known 
as  the  "Brown  Agitator,"1  was  first  introduced  at  Komata  Reefs, 
New  Zealand.  It  acts  on  the  principle  of  the  air  lift.  The  vat  used 
is  a  long,  narrow,  vertical,  cylindrical  vessel,  with  conical  bottom, 
from  40.  to  55  ft.  high  and  10  to  15  ft.  diameter,  with  a  central 
column  1  in.  in  diameter  for  every  foot  of  vat  diameter,  both 
ends  of  which  are  open  and  immersed  in  the  pulp.  Air  is  intro- 
duced through  a  narrower  pipe  opening  at  the  bottom  of  the 
center  column,  at  just  such  a  pressure  as  will  overcome  the  weight 
of  a  column  of  slime-pulp  at  the  point  of  introduction,  thus  estab- 
lishing a  circulation  of  the  slime.  The  power  required  is  2^  h.p. 
per  charge  of  50  tons,  which  would  be  about  the  slime  content  of 
a  40  X  10  ft.  vat.  Apparatus  on  this  principle  has  been  intro- 
duced at  the  Waihi  and  Waihi  Grand  Junction,  New  Zealand; 
also,  as  above  mentioned,  at  Pachuca,  Mexico. 

(C)    ANDREW  F.  CROSSE'S  SLIME  TREATMENT  PROCESS 

The  slime,  after  collection  by  any  suitable  method,  with  addi- 
tion of  the  necessary  amount  of  lime  and  removal  of  excess  of 
water,  is  washed  by  weak  cyanide  solution  into  a  vessel  consisting 
of  two  concentric  steel  cones,  each  having  an  angle  of  45°.  The 
inner  cone  has  a  comparatively  large  opening  at  the  bottom;  its 
sides  are  parallel  with  those  of  the  outside  cone,  and  its  diameter 
about  half  that  of  the  outside  cone.  This  inside  cone  acts  as  a 
baffle  between  the  pulp,  which  is  being  agitated  within  it,  and 
the  outside  portion,  which  is  quiescent  on  the  surface;  it  is  sus- 
pended on  two  girders  resting  on  the  top  of  the  outside  cone.  An 
air-lift  in  the  center  of  the  apparatus  reaches  nearly  to  the  bottom 
of  the  outside  cone;  the  air  pipe  for  working  this  passes  through 
the  bottom  of  the  cone,  at  which  point  there  is  also  a  suitable 
discharge  pipe  and  cock. 

The  upper  end  of  the  air-lift  pump  is  several  feet  above  the 
surface  of  the  pulp,  and  the  overflow  runs  into  a  cylinder  having 
two  or  more  horizontal  discharge  pipes,  so  arranged  that  the 
discharged  pulp  causes  the  pulp  in  the  inside  cone  to  revolve 

i  "  Min.  Sc.  Press,"  XCV,  689. 


212  THE  CYANIDE  HANDBOOK 

and  mix  with  the  clear  solution  returning  from  the  zinc-box. 
The  slime-pulp,  mixed  with  cyanide  solution,  is  pumped  or  run 
into  the  inside  cone,  and  as  soon  as  this  pulp  reaches  half-way 
up  the  air-lift  pump,  the  air  valve  is  opened,  to  prevent  any 
settlement  of  slime.  As  the  slime-pulp  rises  in  the  vat,  the 
outside  portion  tends  to  settle  and  leaves  several  inches  of 
quite  clear  liquid  on  the  surface.  The  pulp  is  allowed  to  flow 
in  until  the  cone  is  nearly  full,  then  the  two  decanting  arms  are 
lowered,  and  the  clear  liquid  drawn  off  and  run  through  a  zinc- 
box  adjoining  the  vat  at  a  slightly  lower  level.  The  effluent 
from  the  zinc-box  is  returned  by  a  small  pump  to  the  inside 
cone,  the  whole  process  being  thus  very  simple.  A  by-pass  is 
provided  to  allow  the  clear  decanted  solution  to  circulate  with- 
out going  through  the  zinc-box,  as  the  first  liquid  drawn  off 
would  contain  no  gold  or  silver.  The  time  required  for  solu- 
tion and  extraction  depends  on  the  nature  of  the  material 
treated.  The  whole  process  is  practically  automatic  and  one 
shiftsman  can  attend  to  a  number  of  vats.  After  treatment, 
the  pulp  is  discharged  into  a  settling  tank  and  the  clear  liquid 
decanted  from  the  settled  pulp.  If  necessary,  the  strong  cya- 
nide may  be  displaced  by  a  weak  solution  by  allowing  the 
liquid  leaving  the  zinc-box  to  run  into  a  sump  and  running  in 
a  very  weak  solution  at  the  same  rate,  so  as  to  displace  the  stronger 
solution.  This  would  be  necessary  in  treating  silver  ores. 

Successful  experiments  with  this  method  have  been  made  at 
Frankfort  (near  Pilgrim's  Rest,  Transvaal)  and  at  Johnson  &  Sons' 
smelting  works,  Finsbury,  London.  The  advantages  claimed  are: 
high  percentage  extraction  of  gold  and  silver;  simplicity  and 
cheapness  in  working;  very  great  saving  in  capital  outlay. 

(D)    TREATMENT  OF  SLIMES  BY  SETTLEMENT  AND  DEC  ANT  ATI  ON 

This  system  was  for  several  years  the  only  one  adopted  on 
the  South  African  gold-fields,  and  even  to-day  it  is,  in  many 
parts  of  the  world,  the  only  method  economically  possible  for 
handling  very  low-grade  material  that  cannot  be  treated  by 
percolation.  It  involves  the  use  of  large  volumes  of  liquid,  and 
consequently  is  not  well  adapted  for  countries  like  Western 
Australia,  where  water  is  very  scarce. 

The  method  consists  of  successive  agitation  with  cyanide 
solution,  settlement  and  decantation,  the  cycle  of  operations  being 


AGITATION  213 

repeated  twice  or  three  times,  and  in  exceptional  cases  oftener. 
The  extraction  obtained  by  each  cycle  depends  (1)  on  the  pro- 
portion of  the  total  value  which  goes  into  solution  under  the 
given  conditions;  (2)  on  the  relative  volumes  of  the  clear-settled 
liquid  and  the  moisture  retained  in  the  residual  pulp  after  de- 
cantation,  it  being  assumed  that  the  dissolved  values  are  dis- 
tributed uniformly  throughout  the  whole  mass  of  liquid;  (3)  on 
the  values  originally  present  in  the  solution  added;  as  the  pre- 
cipitation is  not  absolutely  perfect,  some  gold  and  silver  will 
always  be  present  in  the  liquid  used.  Suppose,  for  example,  the 
slime  to  carry  originally  5  dwt.  per  ton,  of  which  4.5  dwt.  are 
actually  dissolved  during  the  agitation  and  settlement  stages  of 
treatment,  and  that  the  cyanide  solution  used  in  the  proportion  of 
4  tons  solution  to  1  of  dry  slime  carries  originally  0.6  dwt.  per 
ton.  The  settled  slime  after  decantation  retains,  say,  50  per  cent, 
of  moisture.  The  total  value  dissolved  consists  of  4.5  dwt.  per 
ton  of  dry  slime,  distributed  over  4  tons  of  solution,  or  1.125  dwt. 
per  ton  of  solution,  which  in  addition  to  the  0.6  dwt.  originally 
present  gives  1.725  dwt.  The  total  gold  drawn  off  is  therefore 
3  X  1.725  =  5.175  dwt.  per  ton  of  dry  slime  treated.  The 
value  left  in  the  residue  consists  of  1  ton  dry  slime  carrying  0.5 
dwt.,  with  1  ton  solution  carrying  1.725  dwt.,  or  2.225  dwt.  per 
ton  of  dry  slime.  The  extraction,  based  on  original  contents 
of  dry  slime,  is  therefore  5  —  2.225  =  2.775  dwt.,  or  55.5  per 
cent. 

Suppose  now  that  a  second  treatment  is  given  with  3  tons  of 
solution  carrying  0.4  dwt.  per  ton.  This,  with  the  1  ton  of  solu- 
tion carrying  1.725  dwt.  remaining  after  the  first  decantation, 
gives  after  agitation  and  settlement  4  tons  of  solution  carrying 
0.731  dwt.  per  ton,  assuming  that  no  further  dissolution  of  gold 
takes  place.  Then  if,  as  before,  the  settled  residue  retains  50 
per  cent,  of  moisture,  the  result  is  3  tons  of  solution  drawn  off, 
carrying  3  X  0.731  =  2.193  dwt.,  and  a  residue  consisting  of  1 
ton  dry  slime  at  0.5  dwt.  and  1  ton  solution  at  0.731  dwt.,  or  a 
total  of  1.231  dwt.  per  ton  of  dry  slime,  bringing  the  total  extrac- 
tion by  two  treatments  up  to  75.4  per  cent. 

This  example  will  serve  to  illustrate  some  of  the  weak  points 
in  the  decantation  system.  It  is  obvious  that  a  high  extraction 
can  only  be  obtained  by  a  number  of  successive  decantations, 
which  involves  the  handling  of  a  very  large  volume  of  liquid  per 


214  THE  CYANIDE   HANDBOOK 

ton  of  material  treated.  Ample  storage  room  must  be  provided 
for  the  solutions,  so  that  the  first  cost  of  the  plant  is  very  con- 
siderable. Good  extractions,  also,  can  only  be  obtained  by 
using  solutions  from  which  the  values  have  been  very  perfectly 
precipitated  before  use  in  the  slime  tanks. 

The  percentage  of  moisture  in  the  residues  may  be  materially 
reduced  and  the  extraction  correspondingly  improved  by  the 
use  of  very  large,  deep  tanks,  generally  with  a  pointed  bottom. 
After  one  or  two  treatments  by  agitation  and  decantation,  as 
already  described,  the  pulp  is  transferred  to  the  large  tank.  When 
several  charges  have  been  thus  introduced,  the  settled  material 
at  the  bottom  is  under  very  great  hydrostatic  pressure  and  may 
be  withdrawn  as  a  very  thick  pulp  carrying  40  per  cent,  or  less  of 
moisture.  There  is  also  an  additional  economy  in  the  use  of 
these  deep  tanks;  as  the  final  settlement  takes  place  in  them 
instead  of  in  the  agitation  tanks,  the  latter  are  set  free  for  the 
treatment  of  fresh  charges  sooner  than  would  otherwise  be  the 
case.  This  system  was  first  suggested  by  Charles  Butters,  and 
has  been  carried  out  on  a  large  scale,  both  on  the  Rand  and  in 
other  districts. 

By  making  the  final  settlement  tank  sufficiently  large  and 
introducing  the  pulp  by  means  of  a  pipe  passing  some  distance 
below  the  surface  of  the  liquid  contained  in  the  tank,  the  process 
may  be  made  continuous,  the  apparatus  thus  acting  as  a  spitz- 
kasten  and  allowing  clear  liquor  to  overflow  at  the  periphery, 
while  the  thickened  slime  is  constantly  drawn  off  at  the  bottom. 
Several  systems  of  treating  slime  by  continuous  settlement  have 
been  devised,  in  which  this  principle  is  utilized.  One  has  been 
described  by  E.  T.  Rand.1  After  removal  of  superfluous  water 
by  means  of  spitzkasten,  the  thickened  pulp  is  first  agitated 
with  cyanide  solution,  then  pumped  to  a  settling-vat  of  suitable 
size  and  form,  the  thickened  underflow  from  which,  mixed  with 
fresh  solution,  goes  to  a  second  settling-vat.  The  clear  solution 
overflow  from  the  first  settler  goes  direct  to  the  precipitation 
box;  that  from  the  second  settler  goes  to  the  launder  that  feeds 
the  agitation  vat,  and,  with  addition  of  fresh  cyanide,  forms  the 
dissolving  solution.  The  precipitated  liquor  is  pumped  to  the 
launder  by  which  the  pulp  passes  from  the  first  to  the  second 
settler,  and  forms  the  final  wash. 

1  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  686  (1899). 


AGITATION  215 

The  Clancy  system  *  is  very  similar  in  general  design,  but  the 
agitation  tank  is  dispensed  with  and  more  settlers  are  used. 
None  of  these  methods  appears  to  have  come  into  general  use, 
probably  owing  to  the  difficulty  of  obtaining  constantly  a  residue 
sufficiently  low  in  solution  contents  to  be  economically  discharged; 
it  is  not  likely  that  the  final  residue  would  average  as  little  as 
50  per  cent,  moisture,  a  condition  easily  attained  with  the  ordinary 
settlement  and  decantation  process. 

i "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  741. 


SECTION  III 
FILTRATION  BY  PRESSURE  AND  SUCTION 

(A)    ADVANTAGES  OF  THE  SYSTEM 

As  already  pointed  out,  the  methods  of  treating  slime  or 
finely  divided  ore  by  settlement  and  decantation  involve  the  use 
of  tanks  of  large  capacity  for  the  settlement  of  the  pulp  and  for 
the  storage  of  solutions.  It  has  been  shown  also  that  a  high 
extraction  could  be  obtained  only  by  repeating  the  cycle  of 
operations  several  times.  By  using  some  method  of  filtration  by 
pressure  or  suction,  the  greater  part  of  the  dissolved  values  may 
be  extracted  in  one  operation,  in  far  less  time  and  with  the  aid 
of  a  much  smaller  quantity  of  solution  than  is  required  for  the 
decantation  system.  In  the  latter  system,  much  more  time  is 
consumed  in  separating  the  solution  carrying  the  values  from 
the  insoluble  residue  than  in  actually  dissolving  these  values; 
whereas  by  the  system  now  to  be  described  the  separation  of  so- 
lution from  pulp  may  be  made  with  little  delay  as  soon  as  a  suffi- 
cient percentage  of  the  values  has  been  dissolved. 

On  the  other  hand,  the  expense  of  maintenance  and  repairs 
and  the  cost  of  labor  and  supervision  are  probably  very  much 
higher  for  any  system  of  pressure  or  suction  filtering  than  for  the 
decantation  process.  Consequently  the  latter  is  almost  invariably 
adopted  where  finely  divided  low-grade  material  has  to  be  dealt 
with.  In  the  filter  processes  the  quantities  of  material  dealt  with 
in  one  operation  are  necessarily  very  much  smaller  than  in  the 
decantation  process. 

(B)    FILTER-PRESSES 

General  Principles.  —  Filter-presses  consist  essentially  of  a 
number  of  cells  or  elements  into  which  the  material  to  be  filtered 
is  forced  by  hydraulic  or  atmospheric  pressure.  These  chambers 
are  lined  internally  with  filter-cloths,  through  which  the  filtered 

216 


FILTRATION   BY  PRESSURE  AND  SUCTION  217 

liquid  is  forced  as  a  result  of  this  pressure,  passing  out  through 
channels  in  the  walls  of  the  cells,  either  to  separate  outlets  or  to 
a  common  solution-outlet  channel. 

Details  of  Filter-press  Construction.  —  The  following  account  is 
condensed  from  a  description  given  by  Clement  Dixon.1  "A 
filter-press  consists  of  a  number  of  hollow  frames  (from  30  to  50 
in  a  6-ton  press)  placed  alternately  between  solid  flanged  plates, 
with  filter-cloths  of  strong  duck  material  between  each.  The 
hollow  frames  in  a  6-ton  press  would  be  3  ft.  6  in.  or  4  ft.  square 
inside,  and  2,  3,  or  4  in.  in  depth  or  thickness,  as  required  for 
the  particular  ore  treated.  It  will  thus  be  seen  that  we  have 
in  reality  a  number  of  little  vats  standing  on  end,  the  hollow 
frames  forming  the  sides,  and  the  solid  plates  and  filter-cloths 
the  bottoms.  Each  of  the  hollow  frames  (which  receive  the  slimes) 
is  connected  by  a  slot  with  the  slimes  inlet  passage,  and  every 
alternate  solid  plate  is  connected  by  a  slot  with  the  wash-solu- 
tion inlet  passage;  these  solid  flanged  plates  act  as  filter-bottoms 
for  admitting  wash  solutions  to  the  slime  cakes.  The  remaining 
solid  plates  are  connected  with  the  wash-solution  outlet  passage 
and  serve  to  carry  away  the  wash  solution  after  it  has  passed 
through  the  slime  cakes.  On  each  of  the  solid  flanged  plates  is 
a  cock,  used  for  draining  the  press  when  filling  same  with  slimes." 

This  description  applies  to  the  Dehne  and  other  similar  types 
of  press,  which,  however,  show  various  modifications  in  the  less 
important  details  of  construction.  Illustrations  are  here  given  of 
the  plates  and  frames  used  in  the  "  Cyanippus  "  press,  furnished  by 
the  Cyanide  Plant  Supply  Co. ;  in  this  type  the  use  of  drainage 
cocks  for  the  separate  chambers  is  dispensed  with.  In  these 
figures  a  is  the  channel  through  which  the  slimes  pulp  is  intro- 
duced and  which  is  connected  only  with  the  frames  (Fig.  32); 
b  is  the  channel  for  introducing  wash  solution,  and  is  con- 
nected only  with  each  alternate  plate  (those  known  as  high- 
pressure  plates  (Fig.  31);  c  is  the  channel  which  receives  the 
solution  that  has  been  forced  out  through  the  filter-cloths  in  the 
case  of  the  high-pressure  plates;  d  is  a  separate  channel  serving 
as  an  outlet  for  the  filtered  solution  on  the  low-pressure  plates  only 
(Fig.  30) .  A  general  view  of  filter-presses  in  use  for  treatment  of 
slimes  at  Lake  View  Consols,  West  Australia,  is  also  given  (Fig. 
33). 

1  "Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  III,  13. 


218 


THE  CYANIDE  HANDBOOK 


FIG.  30.  —  Cyanippus  Filter  Press,  Low-pressure  Plate. 


FIG.  31.  —  Cyanippus  Filter  Press,  High-pressure  Plate. 


FIG.  32.  —  Cyanippus  Filter  Press.     Frame. 


FILTRATION   BY  PRESSURE  AND   SUCTiON 


219 


To  facilitate  the  passage  of  solution  through  the  cloths,  the 
surfaces  of  the  plates  are  grooved  or  corrugated.  Some  mechanical 
arrangement  is  also  required  for  tightening  the  plates  and  frames 
while  the  press  is  in  use.  This  is  generally  done  by  means  of 
screws  and  levers  at  one  end  of  the  press. 


FIG.  33.  —  Filter  Press  Slimes  Plant  at  Lake  View,  Consols,  W.  Australia. 
Showing  type  of  press  furnished  by  the  Cyanide  Plant  Supply  Co. 

Methods  of  Filling  Filter-presses.  —  Although  some  solution  of 
gold  and  silver  ntay  take  place  during  the  process  of  pressing,  it 
is  generally  better  practice  to  make  sure  that  a  sufficient  percentage 
has  been  dissolved  before  transferring  to  the  presses.  Hence 
some  system  of  agitation  is  commonly  employed,  after  which 
the  pulp,  thickened  to  the  proportion  of  about  one  part  dry  slime 
to  one  part  of  solution,  is  forced  by  compressed  air  or  otherwise 
into  the  filter-presses.  For  this  purpose  a  montejus,  an  air- 
tight cylindrical  vessel,  is  often  used.  This  is  provided  with 
inlets  at  the  top  for  the  pulp  and  compressed  air,  and  an  outlet 
pipe,  reaching  nearly  to  the  bottom,  for  conveying  the  pulp  to 
the  slime-pulp  feed  channels  of  the  presses.  The  pressure  re- 
quired may  be  from  30  to  75  or  even  100  Ib.  per  square  inch. 

In  other  cases  the  presses  are  filled  by  means  of  a  pump;  the 
pumping  is  continued  until  the  cells  of  the  press  are  filled  with 


220  THE  CYANIDE  HANDBOOK 

slime  under  a  sufficient  pressure  to  give  an  efficient  filtration  — • 
say  75  to  80  Ib.  per  square  inch.  It  is  important  to  increase  the 
pressure  steadily  and  uniformly;  hence  some  form  of  air  chamber 
is  commonly  necessary. 

Treatment  in  the  Press.  —  After  the  solution  originally  present 
in  the  pulp  has  been  forced  out  as  much  as  possible,  the  pulp 
inlet  channel  is  closed  and  fresh  solution  is  forced  in  under  pres- 
sure by  means  of  a  pump.  This  passes  by  the  solution  inlet 
channel  (b,  Fig.  31)  into  the  chambers  of  the  presses  and  through 
the  slime  cakes,  passing  out  through  the  outlet  channels  c  and  d 
(Figs.  30  and  31).  Wash-water  may  subsequently  be  introduced 
in  the  same  way,  and  continued  until  the  effluent  is  sufficiently 
low  in  values.  In  some  presses  a  special  inlet  channel  for  wash- 
water  is  provided.  Arrangements  are  also  made  by  which  com- 
pressed air  may  be  forced  into  the  press,  in  order  to  remove  as 
much  liquid  as  possible  at  the  end  of  the  operation.  It  is 
stated  that  by  this  means  the  residual  moisture  may  be  reduced 
in  some  cases  from  25  to  about  14  per  cent. 

Discharging  Filter-presses.  —  When  the  operation  is  complete, 
the  closing-screw  of  the  press  is  loosened  and  the  plates  and  frames 
drawn  apart.  The  slime-pulp  remains  usually  in  the  frames  in 
the  form  of  a  square  cake,  which  is  discharged  by  tilting  or  tapping 
the  frame,  dropping  the  pulp  through  a  discharge  hopper  into 
trucks  running  beneath  the  presses.  After  each  set  of  operations, 
the  plates,  frames,  and  filter-cloths  are  washed  and  cleaned,  and 
the  press  again  closed  ready  for  a  fresh  charge. 

Capacity  of  Filter-presses.  —  The  size  varies  greatly  according 
to  the  work  required.  There  may  be  20  to  50  frames,  with  a 
total  capacity  equal  to  1  to  5  tons  of  dry  slime  per  press  charge. 
In  West  Australia  an  average  of  6  charges  are  treated  per  day  in 
each  press,  one  cycle  of  operations  occupying  4  hours.1 

Where  conditions  allow,  the  discharge  of  the  treated  slimes 
may  be  made  by  sluicing.  In  The  Merrill  Press,2  designed  by 
C.  W.  Merrill  and  introduced  at  various  plants  in  the  Black 
Hills,  South  Dakota,  arrangements  are  made  for  introducing 
water  under  pressure,  whereby  the  treated  slime  may  be  sluiced 
out  of  the  frames  without  opening  the  press.  The  following 
particulars  relating  to  this  type  of  press  are  summarized  from 

1  Julian  and  Smart,  loc.  cit.,  p.  258. 

2  "  Eng.  and  Min.  Journ.,"  LXXXI,  76  (1906). 


FILTRATION   BY  PRESSURE  AND  SUCTION  221 

an  account  given  by  F.  L.  Bosqui.1  The  press  is  of  a  common 
flush  plate  and  distance-frame  pattern,  but  consists  of  larger 
units,  the  dimensions  being: 

Number  of  frames 92 

Size  of  frame      4  X  6  ft. 

Length  of  press    45    ft. 

Capacity    26  tons 

Weight  of  press    65  tons 

Thickness  of  cake    4  in. 

In  addition  to  the  ordinary  channels  for  introducing  slime- 
pulp  and  solution,  there  is  provided  at  the  bottom  of  the  frames 
a  continuous  channel,  within  which  lies  a  sluicing  pipe  with  nozzles 
projecting  into  each  compartment.  This  pipe  can  be  revolved 
through  an  arc  of  any  magnitude,  so  as  to  play  a  stream  into  any 
part  of  the  cake,  washing  it  down  into  the  outlet  channel.  When 
the  press  is  being  filled,  and  during  the  cyanide  treatment,  the 
discharge  ends  of  the  pipe  are  sealed. 

The  mode  of  operating  is  as  follows:  The  slime-pulp,  3  parts 
water  to  1  of  solids,  is  charged  by  gravity  to  the  presses  under 
about  30  Ib.  pressure.  The  cyanide  treatment  is  carried  out  in 
the  press  itself,  the  effluent  solution  going  to  four  precipitating 
vats,  where  the  gold  is  recovered  by  zinc-dust.  There  is  no 
power  cost  for  agitating  or  elevating  slime-pulp,  but  only  for 
elevating  solution  to  the  press.  The  quantity  of  solution  required 
is  0.6  ton  per  ton  of  dry  slime,  of  which  only  0.3  ton  is  precipitated. 
The  power  required  is  TV  h.p.  per  ton  of  dry  slime  treated.  Four 
tons  of  water  per  ton  of  slime  are  required  for  sluicing.  All 
filtering  is  done  by  gravity,  at  a  cost  of  2  cents  per  ton.  In  ex- 
perimental tests  on  this  system  a  recovery  of  91  per  cent,  of  the 
original  value  of  the  slime  was  obtained. 

(C)    FILTRATION  BY  SUCTION 

Early  Applications.  —  As  already  mentioned  in  Section  II,  A, 
the  principle  of  suction  as  an  aid  to  filtration  was  employed  at 
an  early  stage  in  the  development  of  the  cyanide  process.  In 
the  first  plant  where  the  treatment  of  slimes  was  attempted  on 
a  working  scale,  namely  at  the  Robinson  slime  plant,  erected  by 
Charles  Butters,2  the  slime  pulp,  after  being  agitated  sufficiently 

»  "  Min.  Sc.  Press,"  Dec.  15,  1906. 

2  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  241  (Feb.  1898). 


222  THE  CYANIDE   HANDBOOK 

to  dissolve  the  gold,  was  run  on  to  a  filter-vat,  provided  with 
stirring  gear  that  could  be  raised  or  lowered;  the  material  was 
allowed  to  settle,  the  clear  liquid  was  decanted  from  above,  while 
at  the  same  time  suction  was  applied  below  the  filter-cloth.  By 
this  means  about  10  tons  of  slimes  could  be  settled,  decanted 
and  sucked  dry  by  a  vacuum  pump  to  about  28  per  cent,  of 
moisture,  and  would  remain  on  the  filter-cloth  as  a  tough  leathery 
layer  about  6  to  8  in.  thick.  Fresh  solution  was  applied  and  the 
paddle  gradually  lowered  while  revolving  at  the  rate  of  about 
16  r.p.m.,  so  that  in  half  an  hour  the  slimes  were  washed  into  a 
pulp  again.  After  further  dilution,  the  process  of  simultaneous 
settlement,  decantation,  and  suction  by  vacuum  pump  was  re- 
peated. The  method  was  abandoned  owing  to  the  wear  and 
tear  on  the  filter-cloths  and  the  cost  of  keeping  the  suction  pumps 
in  order,  together  with  the  power  and  attention  required  for 
running  them. 

Filtration  aided  by  suction  is  used  also  in  some  cases  in  the 
treatment  of  fine  sands  by  percolation  and  in  the  direct  cyaniding 
of  dry-crushed  ore.  For  this  purpose  the  material  is  generally 
treated  in  comparatively  shallow  vats  and  suction  applied  by 
the  use  of  a  steel  cylinder  connected  with  the  bottom  of  the  tank, 
below  the  filter-cloth,  by  a  pipe,  furnished  with  a  cock.  This 
cylinder  is  also  connected  with  a  vacuum  pump  by  a  separate 
pipe.  The  communication  with  the  tank  is  first  shut  off  and 
the  steel  chamber  exhausted  by  the  vacuum  pump.  The  valve 
connecting  with  the  latter  is  then  closed  and  the  cock  below  the 
filter-tank  is  opened,  the  solution  from  the  latter  being  sucked 
into  the  exhausted  cylinder.  The  advantage  of  this  arrange- 
ment is  that  the  solution  from  the  tank  does  not  pass  direct 
through  the  vacuum  pump,  so  that  the  valves  of  the  pump  are 
not  liable  to  injury  from  grit  passing  through  the  filter. 

The  Moore  Filter.  —  Among  the  more  modern  appliances  for 
filtering  by  means  of  suction  may  be  mentioned  the  Moore  filter, 
the  salient  feature  of  which  is  that  the  filtering  apparatus  is 
movable  and  is  transferred  from  one  tank  to  another  as  required. 
The  following  description  is  quoted  from  an  article  by  R.  Oilman 
Brown,  on  "  Cyanide  Practice  with  the  Moore  Filter/'1  The 
filter  consists  of  a  frame  or  "basket"  carrying  a  number  of 
"plates."  Each  plate  is  composed  of  a  double  thickness  of 

1  "  Min.  Sc.  Press,  Sept.  1,  1906. 


FILTRATION   BY  PRESSURE  AND   SUCTION  223 

canvas,  of  medium  quality,  5  X  16  ft.,  sewed  around  three  edges. 
The  fourth  (long)  edge,  forming  the  top  of  the  filter,  is  bolted 
between  strips  of  wood  1^  X  6  in.  section.  In  the  bottom  edge 
of  each  filter-plate  is  a  J-in.  channel-iron  which  serves  as  a  launder 
for  collecting  the  filtered  solution.  The  filters  are  stitched  ver- 
tically through  both  sides  at  4  in.-distances,  and  in  the  compart- 
ments so  formed  are  placed  J  X  1  in.  strips  to  allow  circulation. 
Each  plate  is  provided  with  a  1-in.  vertical  suction  pipe,  dipping 
into  the  launder  at  the  bottom,  the  end  of  the  pipe  being  flattened 
for  this  purpose.  The  upper  end  of  this  pipe  is  connected  by 
means  of  suction  hose  with  a  3-in.  manifold  and  vacuum  pump. 
There  are  49  of  these  plates  in  each  basket. 

The  mode  of  operation  is  as  follows.  The  basket  is  lowered 
into  a  vat  full  of  pulp  until  the  upper  edge  of  the  plates  is  sub- 
merged. The  suction  pump  is  then  started.  If  the  solution 
drawn  through  is  at  first  muddy,  it  is  returned  to  the  vat.  In 
order  readily  to  locate  any  leaks  in  the  filter-plates,  a  glass  nipple 
is  placed  on  the  pipe  connecting  each  plate  with  the  manifold; 
any  plate  showing  leakage  may  thus  be  at  once  cut  off.  Suction 
is  maintained  with  intermittent  agitation  till  a  sufficient  coat  of 
slime,  averaging  f  in.,  is  obtained,  the  time  required  being  about 
one  hour.  The  basket,  with  the  suction  pump  still  running,  is 
then  raised  by  a  traveling  crane,  transferred  to  a  wash  tank  and 
lowered  therein.  Water  is  sucked  through  the  slime  layer  ad- 
hering to  the  plates  until  the  effluent  is  sufficiently  low  in  cyanide 
(approximately  0.0075  per  cent.),  about  0.7  tons  of  wash-water 
being  needed  per  ton  of  dry  slime.  The  cake  then  contains  40 
per  cent,  of  moisture.  The  basket  is  now  raised  again  and  trans- 
ferred to  the  discharge  hopper;  the  suction  is  continued  until 
excess  of  moisture  is  removed;  the  action  is  then  reversed  and  an 
air  pressure  of  35  Ib.  per  square  inch  given  in  successive  blasts 
for  a  few  seconds,  causing  the  cakes  to  drop  off.  The  residual 
moisture  is  about  32  per  cent.  When  it  is  necessary  to  clean  the 
filters,  water  pressure  instead  of  air  is  applied  until  the  pores  of 
the  cloth  are  freed  from  slime.  This  is  done  about  every  alter- 
nate day. 

In  some  cases  a  second  cyanide  treatment  is  given  before 
water-washing.  The  apparatus  is  charged  with  thick  slime- 
pulp  in  the  first  tank,  transferred  to  a  second  containing  weak 
solution,  where  the  suction  is  continued  for  a  time,  say  20  to  40 


224  THE  CYANIDE  HANDBOOK 

minutes,  then  to  the  water  tank,  and  finally  to  the  discharge 
hopper.  In  general,  it  is  found  that  water  pressure  is  preferable 
to  air  for  discharging,  as  it  brings  the  slime  cake  off  in  one  mass 
instead  of  in  patches.  One  of  the  difficulties  encountered  in 
using  this  system  was  the  imperfect  adhesion  of  the  slime  during 
transfer,  owing  to  jarring  and  partial  drying.  This  caused  un- 
even suction  and  consequent  poor  extraction. 

Among  the  plants  where  the  Moore  system  was  first  adopted 
may  be  mentioned  the  Lundberg  and  Dorr  Mill,  Terry,  South 
Dakota;  the  Liberty  Bell,  Colorado,  and  the  Standard,  Bodie, 
California.  It  was  originally  introduced  by  G.  Moore  at  the  Con- 
solidated Mercur  mines,  Utah,  in  1902  or  1903. 

The  Butters  Filter.  —  This  apparatus  is  in  many  respects 
similar  to  the  Moore  filter.  The  two  systems  have  the  following 
points  in  common:  (1)  The  filtering  apparatus  is  immersed  in 
the  p'ulp  that  is  to  be  filtered;  (2)  the  solution  is  withdrawn  by 
suction,  by  the  use  of  a  vacuum  pump;  (3)  the  cakes  of  slime 
formed  adhere  to  the  outside  of  the  filter-plates;  (4)  a  large 
filtering  area  is  obtained  in  a  cheap  and  compact  form. 

The  essential  difference  is  that  in  the  Butters  system  all  the 
operations  are  conducted  in  one  vat.  The  filter  itself  is  station- 
ary, but  so  arranged  that  the  separate  plates  or  "leaves"  may 
be  lifted  out  if  necessary.  The  pulp  is  first  brought  to  the  proper 
consistency  by  settlement  and  decantation;  the  thickened  pulp 
is  then  run  into  a  special  rectangular  filter-box,  in  which  the 
apparatus  is  suspended.  Suction  is  applied  until  a  sufficient 
coating  of  slime  is  obtained ;  the  surplus  pulp  is  then  withdrawn 
from  the  filter-box  by  suitable  pumps  arid  returned  to  the  settling 
tank  or  slime  reservoir.  The  box  is  now  filled  with  weak  cyanide 
solution,  which  is  sucked  through  as  long  as  may  be  necessary 
for  extraction  of  the  values.  The  surplus  solution  is  then  pumped 
back  to  the  storage  tank,  water  substituted,  and  suction  con- 
tinued till  soluble  values  are  extracted.  Finally,  the  suction  is 
cut  off,  water  pressure  is  applied  to  force  off  the  adhering  cakes, 
which  fall  into  the  filter-box  and  thence  through  hoppers  with 
sides  inclined  at  a  sharp  angle,  whence  they  are  discharged  into 
a  launder  by  means  of  a  gate-valve  at  the  apex  of  each  hopper. 
On  closing  the  valves,  the  filter-box  may  be  again  charged  with 
slime-pulp. 

The  construction  of  the  " leaves"  in  this  system  differs  some- 


FILTRATION   BY  PRESSURE  AND  SUCTION  225 

what  from  that  of  the  "  plates  "  in  the  Moore  system.  A  detailed 
description  by  E.  M.  Hamilton  is  given  by  Julian  and  Smart; l 
it  need  only  be  said  here  that  each  leaf  consists  essentially  of  an 
oblong  frame  suspended  from  a  wooden  bar  forming  the  upper 
side  of  the  leaf.  Its  remaining  three  sides  are  formed  by  a  pipe 
bent  at  right  angles  and  perforated  along  its  upper  edge  in  the 
part  forming  the  bottom  of  the  frame.  The  inner  space  is  filled 
with  cocoanut  matting.  The  whole  is  enclosed  in  canvas,  stitched 
vertically  as  in  the  Moore  system,  and  forming  the  filtering  sur- 
face to  which  the  slime  adheres.  The  perforated  pipe  is  closed 
at  one  end  and  communicates  at  the  open  end  with  the  vacuum 
apparatus,  and  also  with  the  water  tank  used  when  water  pres- 
sure is  required  for  discharging. 

The  Butters  filter,  which  is  the  result  of  experiments  carried 
out  by  Charles  Butters  and  staff,  has  been  installed  at  the  Butters 
plant,  Virginia  City,  Nevada;  at  the  Butters  Copala  Syndicate 
Mill.  Mexico;  at  the  Combination  Mill,  Goldfield,  Nevada,  and 
elsewhere.  At  the  first-mentioned  plant  it  is  stated  that  150 
tons  of  slime  are  treated  per  day  at  a  cost  of  11}  cents  per  ton. 

The  Cassel  filter  is  of  very  similar  design  to  the  Butters  filter. 
The  chief  distinction  is  that  the  filter-cloth  is  separately  supported 
on  a  movable  frame.  At  the  end  of  the  operation  the  slime-cake 
is  detached  by  oscillating  this  frame. 

The  following  particulars  of  the  costs  and  power  required 
for  working  the  Butters  system  are  given  by  F.  L.  Bosqui : 2 

At  the  200- ton  plant,  Virginia  City,  Nevada,  10  cents  per  ton; 
At  the  40-ton  plant,  Combination  Mill,  Nevada,  45  cents  per  ton. 

The  latter  could  be  reduced  to  31  cents  per  ton  by  working  the 
plant  at  its  full  capacity  of  56  tons.  Former  cost  of  filter-pressing 
was  $1  per  ton. 

The  power  required  at  the  Combination  Mill  is: 

For  filtering 9  h.p. 

For  agitating  slime-pulp 3    " 

For  pumping  and  other  purposes 9    " 

The  pumps  required  are:  one  4-in.  Butters  centrifugal  pump; 
one  12  X  10-in.  Gould's  vacuum  pump;  one  2-in.  centrifugal 
pump  for  raising  filtered  solution  to  clarifying  filter-press;  and 

»  Loc.  tit.,  p.  246. 

2  "  Min.  Sc.  Press,"  Dec.  15,  1906. 


226  THE  CYANIDE  HANDBOOK 

one  2-in.   centrifugal  pump  for  returning  slime  overflow   from 
leaching  vats  to  slime  settlers.1 

Traveling  Belt  Filters.  —  As  early  as  1893  it  was  suggested 
by  W.  Brunton  to  use  an  endless  traveling  belt  of  filter-cloth, 
passing  over  vacuum  chambers,  for  filtering  slime-pulp,  the  slime 
being  spread  over  the  cloth  at  the  head  of  the  machine.  Several 
other  filters  on  the  same  or  somewhat  similar  lines  have  been 
suggested.2 

THE  CRUSH  FILTERS 

The  courtesy  of  the  Cyanide  Plant  Supply  Co.  permits  the 
following  description  of  these  appliances,  of  which  that  company 
controls  the  patents.  They  are  of  two  types,  distinguished  as 
the  "Traversing  Filter"  and  the  "Fixed  Immersed  Filter." 

The  Crush  Traversing  Filter 

This  system  was  elaborated  by  Barry  and  Banks  at  the  Waihi 
mine,  New  Zealand,  and  in  its  general  features  somewhat  resembles 
the  Moore  filter,  with  the  important  exception  that  no  reverse 
pressure  of  air  or  other  fluid  is  necessary  for  discharging  the  cakes, 
and  that  the  material  to  be  filtered  is  agitated  during  filtration. 

Each  basket  carries  a  number  (generally  ten)  of  filter-plates 
or  leaves  hung  between  two  joists,  and  is  suspended  from  a  traver- 
sing crane,  by  which  it  may  be  raised  or  lowered  and  transferred 
from  the  pulp  tank  to  the  wash  tank  or  to  the  discharge  hopper, 
as  required.  Each  filter-plate  consists  of  a  sheet  of  thin  gal- 
vanized iron,  carried  by  a  wooden  bar  and  enclosed  in  a  frame 
of  iron  piping.  The  whole  is  enveloped  in  cotton  twill  or  duck, 
between  which  and  the  iron  may  be  placed  cocoanut  matting  or 
other  filtering  medium  if  required.  The  plates  are  kept  apart 
by  the  supporting  wooden  bars  or  by  wires  arranged  at  an  angle. 
Each  frame  communicates  by  flexible  rubber  tubes  with  a  main, 
this  being  further  connected  by  flexible  hose  with  a  vacuum 
reservoir  or  pump.  The  frames  are  also  connected  to  another 
main  having  a  valve  opening  to  the  atmosphere.  (See  Figs.  33a 
and  33  b.) 

The  mode  of  operation  is  similar  to  that  of  the  Moore  filter. 

1  As  the  filter-cloths  in  time  become  choked  with  lime  and  other  salts,  it  is 
necessary  at  intervals  to  immerse  the  leaves  in  dilute  hydrochloric   acid,  which 
dissolves  the  deposits  and  thus  restores  the  efficiency  of  the  filter. 

2  See  Julian  and  Smart,  loc.  cit.,  p.  251. 


FILTRATION   BY   PRESSURE  AND   SUCTION 


227 


(See  above.)  When  the  basket  is  lowered  into  the  pulp  tank,  the 
valve  on  the  atmospheric  main  is  left  open  to  allow  the  displaced 
air  to  escape.  As  soon  as  the  filter  is  immersed,  the  valve  on  the 
atmospheric  main  is  shut  off  and  that  on  the  vacuum  main  turned 


FIG.  33a.  —  Crush  Traversing  Filter  immersed  in  Pulp  and 
Solution  Tanks. 

on.     The  pulp  is  agitated  with  compressed  air  or  otherwise  to 
prevent  settlement  during  the  filtering  operation. 

The  time  required  for  formation  of  the  cake  is  30  to  45  minutes, 
and  for  extraction  in  the  wash  tank  about  30  minutes.  The 
whole  cycle  of  operations,  including  charging,  discharging,  and 
transferring,  takes  about  2  hours.  The  cake  varies  in  thickness 
from  J  to  1J  in.  In  discharging,  the  vacuum  is  maintained  until 


228 


THE  CYANIDE   HANDBOOK 


a  crack  begins  to  form  at  the  junction  of  the  supporting  bar  with 
the  corrugated  plates;  the  vacuum  is  then  cut  off  and  air  ad- 
mitted. The  cake  immediately  discharges  itself  with  a  rolling 
motion,  and  after  a  little  cleaning  the  basket  is  ready  for  a  fresh 
charge. 


FIG.  336.  —  Crush  Traversing  Filter,  raised   for  transfer- 
ring or   discharging. 

During  the  drying  operation  before  discharging,  the  inrush  of 
air  has  the  effect  of  lowering  the  vacuum  and  so  interfering  with 
the  suction  on  the  other  baskets;  it  is  therefore  advisable  either 
to  have  a  separate  vacuum  pump  for  each  basket  or  a  separate 
connection  with  high-  and  low-pressure  pumps,  the  latter,  giving 
a  vacuum  of  5  to  10  in.,  to  be  applied  as  soon  as  the  filter  is  raised 
out  of  the  wash  tank  for  discharging. 

The  frames  are  made  in  two  sizes  —  16  X  4  ft.  and  10  X  5  ft., 
with  10  frames  in  each  basket.  Each  basket  of  the  first  type 
treats  40  to  60  tons  of  slime  per  day;  the  filter-cloth  requires 
renewal  about  once  in  6  months,  1  sq.  yard  of  cloth  treating  about 
4  tons  of  slime. 

The  power  required  for  the  crane  is  10  h.p.;  the  vacuum  pump 


FILTRATION   BY   PRESSURE  AND   SUCTION 


229 


requires  6  h.p.  per  basket.     When  air  agitation  is  used,  additional 
power  is  needed.     (See  Figs.  33a  and  336.) 

The  Crush  Fixed  Immersed  Filter 

In  this  type  the  filter  is  stationary  and  the  crane  is  dispensed 
with.  In  principle  it  resembles  the  Butters  and  Cassel  filters. 
The  pulp  is  agitated  in  the  filter-box  by  means  of  centrifugal 
pumps,  and  after  a  sufficient  thickness  of  cake  has  accumulated 
on  the  plates,  the  surplus  pulp  is  returned  to  a  pulp  storage-tank 
(a,  Figs.  34a,  and  346.)  This  type  of  apparatus  is  claimed  to  have 


a  Pulp  Tank 

b  Pulp  Filter 

c  Gold  Solution  Tank 

d  Centrifugal  Pump 

e   Vacuum  Pump 


FIG.  34a.— Plan  of  Crush  Filter  Plant.    (Fixed  immersed  type.) 

the  drawback  that  there  is  a  danger  of  untreated  material  being 
discharged,  as  the  filtration  and  discharge  of  the  slime  both 
take  place  in  the  same  vessel.  This  can  only  be  obviated  by 
carefully  attending  to  the  washing  out  of  the  pulp-box  (b,  Fig. 
34 a),  after  removing  the  surplus  pulp  when  the  cake  has  formed. 
These  washings  should  of  course  be  returned  to  the  general  stock 
in  the  supply  tank,  which,  however,  may  thus  become  unduly 
diluted. 

The  construction  of  the  filter-plates  is  identical  with  that  of 
the  traversing  type  of  filter,  but  no  hessian  or  cocoanut  matting 


230 


THE  CYANIDE   HANDBOOK 


is  used  in  the  leaves,  and  it  is  claimed  that  the  latter  are  not  liable 
to  be  choked  with  lime  or  fine  particles.  It  is  advisable  in  this 
case  also  to  have  high-  and  low-pressure  vacuum  pumps  in  con- 
nection with  the  frames,  the  former  to  be  used  during  the  actual 
filtering  operations  and  the  latter  while  filling  or  emptying  the 
pulp-box.  Too  high  a  vacuum  while  the  plates  are  exposed  to  air 
would  cause  cracks  to  form  in  the  slime  cakes,  rendering  the 
subsequent  washing  inefficient. 

Another  drawback  pointed  out  by  the  Cyanide  Plant  Supply 
Co.  is  the  liability  of  the  cakes  to  drop  off  during  the  rather  long 
period  occupied  in  emptying  the  tank  of  surplus  pulp  and  refill- 
ing with  solution  or  wash-water.  This  renders  the  method  un- 


a  Pulp  Tank 

b  Pulp  Filter 

c   Gold  Solution  Tank 

d   Centrifugal  Pump 

c    Vacuum  Pump 


FIG.  346. — Elevation  of  Crush  Filter  Plant.     (Fixed  immersed  type.) 

suitable  for  sandy  or  granular  matter.  The  difficulty  may  be 
remedied  by  the  use  of  very  large  pumps  for  transferring  pulp 
and  solution,  but  this  adds  greatly  to  the  cost  of  the  installation. 
The  capacity  of  a  standard  plant  on  this  system  is  about  six  to 
eight  charges  per  day,  say  100  tons  of  dry  slime,  or  about  1  ton 
per  day  for  every  30  sq.  ft.  of  filtering  area.  The  power  required 
is  about  9  h.p.  when  the  slime-pulp  is  fed  by  gravity  to  the  filter- 
tank,  and  about  30  h.p.  when  pump  circulation  is  used. 

The  Ridgway  Filter 

A  further  extension  of  the  idea  of  a  traveling  suction-filter, 
first  introduced  in  the  case  of  the  Moore  apparatus,  already  de- 
scribed, is  seen  in  the  Ridgway  filter,  of  which  illustrations  in 
plan  and  section  are  here  given  (Figs.  35  and  36).  The  carriers 
bearing  the  filter-plates  revolve  about  a  central  hollow  axis  and 
travel  along  a  circular  track  in  such  a  way  that  during  part  of  the 
circuit  the  filter-plates  are  immersed  in  slime-pulp.  The  latter, 
containing  the  necessary  amount  of  cyanide  for  dissolution  of  the 
values,  is  fed  continuously  into  a  section  of  the  annular  space 
between  the  tracks,  and  a  portion  of  the  pulp  adheres  to  each 


FILTRATION   BY   PRESSURE  AND   SUCTION 


231 


plate  as  it  passes  through,  hi  consequence  of  the  suction.  Every 
plate  is  connected  by  a  separate  pipe  with  the  central  hollow 
shaft  about  which  the  apparatus  revolves;  this  communicates  with 


FIG.  35.  —  Plan  of  Ridgway  Filter.     [From  illustration  furnished  by  the 
Cyanide  Plant  Supply  Co.] 

the  receiver  of  a  vacuum  pump,  by  which  the  filtered  solution  is 
continuously  withdrawn.  At  a  certain  point  in  the  circuit,  the 
outer  edge  of  the  track  ascends  so  that  the  traveler  rises  out  of 


Compressed  Air 


Strong  Solution 
ounm  Pump 

FIG.  36.  —  Sectional  Elevation  of  Ridgway  Filter. 

the  slime-pulp;  beyond  this  point  it  descends  again  into  a  separate 
section  of  the  annular  trough,  which  is  kept  filled  with  water. 
As  the  filter-plates  travel  through  this  water,  the  latter  is  sucked 
continuously  through  the  adhering  slime  cake,  displacing  the 


232  THE  CYANIDE   HANDBOOK 

solution.  Finally,  the  outer  track  again  rises  so  that  the  carrier 
emerges  from  the  liquid  and  at  the  same  time  the  suction  is 
automatically  cut  off,  and  compressed  air  applied  by  separate 
pipes  connected  with  each  filter-plate.  As  a  result  of  this  pres- 
sure, the  slime  cakes  drop  off  and  are  received  in  a  discharge 
hopper  at  this  point.  The  carrier  then  descends  again  into  the 
section  of  the  apparatus  containing  the  slime-pulp  and  the  cycle 
of  operations  is  repeated.  This  apparatus  is  also  furnished  by 
the  Cyanide  Plant  Supply  Co. 

The  following  additional  particulars  with  regard  to  the  Ridg- 
way  filter  may  be  of  interest.1  The  first  trials  with  the  machine 
were  made  at  the  Great  Boulder  mine,  Kalgoorlie,  West  Australia, 
January,  1906.  There  are  12  to  14  radial  arms  or  levers,  each 
bearing  a  flat  cast-iron  filtering  frame,  corrugated  on  the  under 
surface;  to  these  corrugated  surfaces  screens  are  attached  over 
which  ordinary  filter-cloth  is  fixed,  giving  4  sq.  ft.  of  filtering 
area  per  frame.  The  central  column,  in  its  lower  part,  has  two 
internal  compartments,  each  connected  separately  with  a  vacuum 
pump  and  serving  as  channels  for  withdrawing  the  effluent  gold 
solution  and  wash  solution  respectively.  The  upper  portion  of 
the  column  is  either  connected  with  an  air  compressor  or  is  con- 
structed to  act  as  an  air  compressor,  driven  by  the  machine  itself. 
Each  filtering  frame  is  connected  by  3  radial  pipes  and  rubber 
hose  with  the  two  compartments  of  the  central  column  and  with 
the  compressed-air  section. 

The  outer  ends  of  the  levers  are  provided  with  rollers  running 
along  a  circular  track  at  the  edge  of  the  annular  trough  which 
holds  the  slime-pulp  and  wash-water.  The  frames  are  suspended 
horizontally  from  the  levers  in  such  a  way  that  the  lower  surface 
only  is  immersed;  at  the  points  between  the  sections  of  the  trough, 
where  the  track  is  raised,  the  filtering  frames  emerge  from  the 
liquid,  and  at  the  same  time  one  of  the  three  valves  connecting 
with  the  central  column  is  closed;  on  descending  again,  another 
valve  is  opened.  These  valves  are  automatically  operated  while 
the  machine  is  in  motion  by  small  rollers  passing  over  elevations 
on  one  or  other  of  three  concentric  tracks.  The  series  of  opera- 
tions is  as  follows: 

After  the  frame  has  passed  the  discharge  chute,  it  descends 

*"  Monthly  Journal  Ch.  of  Mines,"  West  Australia,  Nov.,  1906.  See  also 
"Min.  Sc.  Press,"  P'eb.  9,  1907. 


FILTRATION   BY  PRESSURE  AND   SUCTION  233 

into  the  slime-pulp;  at  the  same  time  the  gold-solution  valve  is 
opened  by  a  roller  running  up  an  incline  on  its  track,  opening 
direct  connection  between  the  filter-frame  and  the  vacuum  which 
is  maintained  in  the  center  column.  When  the  frame  ascends 
from  the  pulp,  the  gold  solution  valve  is  closed;  as  it  descends  into 
the  wash  solution,  the  wash  valve  connected  with  the  other 
section  of  the  center  column  is  opened,  causing  the  vacuum  to 
draw  wash  solution  through  the  adhering  pulp.  The  frame  con- 
tinues in  the  wash  trough  for  half  a  circle;  when  it  again  rises, 
the  wash  valve  is  not  closed  till  the  discharge  chute  is  reached, 
so  as  to  allow  the  slime  cake  to  be  extracted  by  suction  as  thor- 
oughly as  possible.  When  the  discharge  chute  is  reached,  the 
wash  valve  closes  and  the  air  valve  opens,  admitting  a  puff  of 
compressed  air,  which  enters  the  filter-frame  and  causes  the  resi- 
due to  drop  off  into  the  chute  and  thence  into  a  truck.  The 
machine  makes  about  one  revolution  per  minute.  Air-tight  con- 
nections between  the  rotating  and  stationary  parts  are  secured 
by  means  of  glands  and  stuffing-boxes. 

The  supply  of  pulp,  wash  solution,  and  water  to  the  annular 
troughs  is  regulated  by  float  valves  in  the  receiving  compart- 
ments, which  are  placed  outside  the  peripheral  track.  The 
pulp  is  kept  from  settling  by  the  revolution  of  small  agitators 
driven  independently  of  the  other  parts  of  the  machine. 

From  0.8  to  1  ton  of  wash  solution  is  used  per  ton  of  dry  slime : 
the  residues  carry  28  to  33  per  cent,  of  moisture,  showing  only  a 
trace  of  dissolved  gold  and  cyanide.  An  extraction  of  89  per  cent, 
is  claimed  in  the  treatment  of  old  battery  slime.  The  vacuum 
pump  requires  3£  h.p.,  the  agitators  1  h.p.,  and  the  filter  machine 
J  h.p.,  making  a  total  of  5  h.p.  The  capacity  is  25  to  66  tons  per 
day,  according  to  the  nature  of  material  treated. 

The  Bertram  Hunt  Filter 

The  following  account  of  this  apparatus  is  summarized  from 
description  given  by  the  inventor.1  The  filter-bed  is  composed 
of  gravel  and  sand,  resting  on  wooden  slats  and  supported  on 
an  annular  concrete  structure,  raised  at  the  edges  2  in.  above 
the  filter-bed.  The  slats  are  i  to  f  in.  apart.  The  top  layer  of 
the  filter  is  composed  of  sand  of  8  to  12-mesh  size,  and  is  one 

»  "  Min.  Sc.  Press,"  XCVII,  430  (Sept.  26,  1908). 


234  THE  CYANIDE  HANDBOOK 

inch  in  thickness.  A  vacuum  filter  is  applied  beneath,  but  no 
filter-cloth  is  used.  A  carriage  bearing  scrapers  revolves  about 
the  central  hollow  pillar,  and  travels  over  the  annular  filter- 
bed,  being  supported  on  the  raised  edges  of  the  concrete  bottom. 
By  means  of  this  carriage,  the  material  to  be  treated  is  con- 
tinuously fed  onto  arid  removed  from  the  filter-bed.  The  appa- 
ratus carries  a  scraper  in  front,  which  removes  the  upper  layer  of 
slime  and  transfers  it  to  a  screw  conveyor,  by  which  it  is  dis- 
charged or  conveyed  to  the  central  hollow  pillar,  whence  it  is 
discharged  by  sluicing.  Behind  the  scraper  is  a  distributor  for 
the  sandy  portion  of  the  pulp,  followed  by  another  for  the  slimy 
portion.  Revolving  pipes  to  spray  solution  and  wash-water  fol- 
low the  carriage  at  suitable  distances. 

The  outside  diameter  of  the  machine  is  15  ft.,  the  annular 
filter-bed  being  3  ft.  wide,  thus  giving  a  filtering  surface  of  113 
sq.  ft.  The  speed  is  1  r.p.m.  Taking  the  quantity  of  material 
discharged  during  each  revolution  as  represented  by  a  layer  J-in. 
thick,  say  2.26  cu.  ft.,  carrying  50  per  cent,  moisture,  or  123  Ib.  of 
dry  residue,  the  capacity  of  the  apparatus  would  be  80  tons  per 
day.  The  power  required  to  drive  the  machine  is  about  1  h.p., 
and  for  the  vacuum  filter  4  h.p.,  or  a  total  of  5  h.p.  It  is  stated 
that  a  clear  filtrate  is  always  obtained. 

Whenever  it  is  desirable  to  clean  the  permanent  filter-bed, 
the  adjustable  scraper  is  lowered  and  the  sand  above  the  slats 
removed.  Clean  sand  is  then  spread  to  the  required  depth.  The 
apparatus  can  be  arranged  with  a  separate  vacuum  for  strong 
and  weak  solutions. 


SECTION  IV 

HANDLING   OF  SOLUTIONS 

(A)  SUMPS  AND  STORAGE  TANKS 

IN  addition  to  the  vats  or  other  vessels  used  for  holding  the 
material  under  treatment,  storage  room  must  be  provided  for 
the  solutions,  before  and  after  use.  The  volume  occupied  by  the 
solution  may  be  taken  as  about  31  to  32  cu.  ft.  per  ton.  The 
volume  occupied  by  ordinary  tailings  varies  from  20  to  about  26 
cu.  ft.  per  ton,  according  to  the  density  with  which  it  is  packed 
into  the  leaching  vats.  It  is  impossible  to  give  any  fixed  rule  as  to 
the  capacity  required  for  storing  solutions,  but  it  may  be  taken 
as  about  equal  to  the  vat  capacity  required  for  the  material 
actually  undergoing  treatment  at  any  one  time.  As  already 
mentioned,  there  are  in  general  three  classes  of  solution,  for 
which  separate  tanks  must  be  provided,  namely,  strong  cyanide, 
weak  cyanide,  and  alkali. 

The  storage  tanks  are  generally  similar  in  construction  to 
the  leaching  tanks,  but  without  filter-frames,  and  may  be  of  wood 
or  iron.  It  is  usual  to  make  them  deeper  in  proportion  to  diameter 
than  the  leaching  tanks,  as  this  form  is  more  economical  in  con- 
struction, and  there  is  in  this  case  no  limitation  of  depth  on  account 
of  difficulties  in  percolation.  They  are  generally  placed  either 
above  the  level  of  the  leaching  vats,  so  that  the  solution  can  pass 
from  them  to  the  latter  by  gravity,  or  below  the  outlet  of  the 
precipitation  boxes,  so  that  the  precipitated  solution  flows  into 
them  by  gravity.  In  the  latter  arrangement  the  storage  tanks 
are  commonly  described  as  "sumps."  In  the  first  case,  arrange- 
ments must  be  provided  for  continuously  pumping  the  precipi- 
tated solution  as  it  leaves  the  boxes  up  to  the  storage  tanks. 
The  solution  flowing  from  the  boxes  runs  into  a  small  cement- 
lined  depression  or  sump  in  the  floor  of  the  extractor  house,  from 
which  it  is  pumped  at  the  same  rate.  In  the  second  case,  with 
the  storage  tanks  below  the  precipitation  boxes,  every  solution 

235 


236  THE  CYANIDE   HANDBOOK 

run  on  to  the  leaching  tanks  must  be  pumped  up,  as  required, 
but  the  pumping  will  not  be  continuous. 

It  is  obvious  that  the  same  amount  of  liquid  must  be  raised 
in  both  cases;  but  in  the  first  case  the  average  hight  of  lift  will 
be  greater,  as  all  the  solution  must  be  raised  from  the  level  of  the 
boxes  to  the  top  of  the  storage  tanks,  whereas  in  the  second  case 
the  average  lift  will  be  from  half  the  depth  of  the  storage  tanks 
to  the  top  of  the  leaching  vats. 

Dissolving  Tank.  —  A  special  small  tank  is  generally  provided 
for  dissolving  the  solid  cyanide  and  preparing  a  concentrated 
solution,  from  which  the  necessary  amount  is  drawn  off  as  re- 
quired for  making  up  the  solutions  in  the  storage  tanks. 

(B)    SETTLING  AND  CLARIFYING  TANKS 

It  frequently  happens,  for  various  reasons,  that  the  solutions 
leaving  the  leaching  vats,  or  decanted  from  slime-settling  tanks, 
and  also  those  drawn  off  from  filter-presses  or  suction  filters,  are 
not  perfectly  clear.  Consequently  it  is  the  usual  practice  to  run 
such  solutions  into  a  separate  tank,  instead  of  allowing  them  to 
flow  direct  to  the  head  of  the  precipitation  box.  When  the  liquid 
has  settled  clear,  it  is  drawn  off  by  syphon  or  otherwise,  and  the 
introduction  of  sand  or  other  suspended  matter  into  the  boxes 
is  avoided.  The  arrangement  has  the  additional  advantage  that 
a  perfectly  regular  flow  of  liquid  through  the  boxes  can  be  main- 
tained, as  the  rate  of  flow  need  not  depend  on  the  rate  of  leaching, 
decanting,  etc.  In  some  cases  it  is  advisable  to  allow  the  solu- 
tions to  percolate  through  a  sufficient  thickness  of  clean  sand, 
in  what  is  described  as  a  clarifying  tank.  Other  materials,  such 
as  cotton  waste,  coir  matting,  etc.,  are  likewise  used  for  clarifying. 
Sometimes  the  solution  is  introduced  from  below  and  caused  to 
percolate  upwards  through  the  clarifying  medium. 

Another  arrangement  sometimes  adopted  is  to  pass  the  liquid 
to  be  clarified  through  a  special  small  filter-press  adapted  for  this 
class  of  work.  An  account  of  this  method  is  given  by  Truscott 
and  Yates.1  Previous  to  the  introduction  of  the  clarifying  press, 
at  Redjang  Lebong,  Sumatra,  slime  had  been  carried  into  the 
zinc-boxes,  notwithstanding  the  use  of  several  successive  settle- 
ment tanks  and  the  addition  of  lime  in  the  launder  from  the  filter- 

1  "  Journ.  Chem.,  Met  and  Min.  Soc.  of  South  Africa,"  VII,  3  (July,  1906). 


HANDLING   OF  SOLUTIONS  237 

presses,  and  caused  much  trouble  and  expense  in  the  smelting  of 
the  precipitate.  It  was  found  that  the  solution  could  be  effectively 
clarified  by  passing  it  through  two  small  Johnson  presses;  these 
were  opened  twice  a  week  and  the  cloths  well  scrubbed  to  free 
the  pores  from  fine  slime.  The  beneficial  effect  of  the  filter-press 
clarification  upon  the  solution  was  at  once  felt  in  the  smelting; 
the  precipitate  became  clean  and  was  easily  reduced,  the  smelting 
costs  being  reduced  from  3.07  pence  to  0.87  pence  per  ounce  of 
fine  metal  recovered. 

(C)    PUMPS 

The  pumps  commonly  used  for  transferring  solutions  or  for 
circulating  slime-pulp  are  centrifugal  pumps,  the  size  varying 
with  the  work  required.  A  4-in.  pump  is  a  convenient  size  for 
many  purposes.  When  the  pumping  required  is  for  the  con- 
tinuous transfer  of  small  quantities  of  solution,  several  small 
pumps,  one  at  least  for  each  class  of  solution,  will  be  needed; 
this  will  be  the  case  when  the  storage  tanks  are  above  the  leach- 
ing tanks.  Where  pumping  is  only  necessary  at  intervals  and 
the  object  is  to  transfer  large  quantities  of  solution  rapidly,  one 
or  more  large  pumps  are  necessary.  This  is  the  case  when  the 
storage  tanks  are  below  the  leaching  vats. 

Pumps  with  brass  or  copper  fittings  should  be  avoided;  all 
parts  liable  to  come  in  contact  with  solution  should  be  of  iron 
or  steel.  For  special  purposes  other  types  of  pump  are  used. 
For  transferring  sandy  or  gritty  material  the  "  air  lift "  is  com- 
monly employed.  Some  account  of  the  Frenier  sand  pump  has 
already  been  given.  (See  Part  III.)  The  power  required  for  trans- 
ferring slime-pulp  is  considerably  greater  than  that  needed  for 
solution. 

(D)    PIPING  FOR  CONVEYING  SOLUTIONS 

Iron  pipes  are  used  for  transferring  solution  (1)  from  the 
storage  tanks  to  the  leaching  tanks,  agitation  tanks,  or  filter- 
presses;  (2)  from  the  treatment  tanks  to  the  precipitation  boxes 
or  clarifying  tanks;  (3)  from  the  precipitation  boxes  to  the  storage 
tanks.  When,  as  is  usually  the  case,  several  different  kinds  of 
solution  are  used,  arrangements  must  be  made  to  convey  each 
class  of  solution  as  required  to  each  treatment  tank.  This  may 
be  done  either  by  having  a  separate  pipe  for  each  class  of  solution, 


238  THE  CYANIDE  HANDBOOK 

with  a  cock  over  each  treatment  tank,  or  by  having  a  common 
"solution  main"  for  all  classes  of  solution,  with  separate  pipes 
and  cocks  between  it  and  the  storage  tanks,  and  also  separate 
branch  pipes  and  cocks  for  each  treatment  tank.  The  latter 
system  is  more  economical  as  regards  piping  and  the  number  of 
cocks  required,  but  is  perhaps  somewhat  more  complicated  in 
actual  working,  as  there  is  more  likelihood  of  mistaking  the  solu- 
tion required;  and  it  also  involves  the  necessity  of  opening  two 
cocks  for  each  transfer. 

When  a  pump  has  to  be  used  for  filling  a  tank  or  transferring 
a  solution  to  a  treatment  tank,  it  is  necessary  to  open  the  cock 
before  starting  the  pump;  otherwise  the  pipe  may  burst  or  the 
driving  belt  of  the  pump  may  be  thrown  off. 

The  pipes  used  for  running  solution  to  the  tanks  should  be 
fairly  large,  so  that  this  operation  may  be  carried  out  as  quickly 
as  possible.  For  conveying  solution  from  the  treatment  tanks 
to  the  settling  or  clarifying  tanks,  or  direct  to  the  precipitation 
boxes,  a  separate  pipe  from  each  treatment  tank  is  desirable, 
so  that  the  nature  of  the  effluent  and  the  rate  of  flow  from  each 
tank  may  be  readily  observed.  Some  arrangement  is  also  neces- 
sary to  divert  the  effluent  as  required  into  any  precipitation 
box.  This  may  easily  be  done  by  means  of  a  length  of  rubber 
hose  at  the  exit  end  of  the  pipe  conveying  solution  to  the  boxes. 
In  some  plants  separate  receivers  or  launders  are  provided  for 
each  class  of  solution,  with  which  the  pipes  from  the  tanks  may 
be  connected  as  required;  these  receivers  are  connected  with  one 
or  more  of  the  boxes  set  apart  for  each  class  of  solution. 

For  conveying  solution  from  the  boxes  to  the  storage  tanks, 
it  is  often  necessary  to  arrange  for  putting  any  box  in  communica- 
tion with  any  of  the  storage  tanks;  the  system  will  therefore  be 
similar  to  that  for  connecting  the  storage  tanks  with  the  treat- 
ment tanks.  In  cases  where  separate  boxes  are  reserved  exclu- 
sively for  one  class  of  solution,  however,  it  is  only  necessary  to 
have  a  single  pipe  connecting  each  box  with  its  appropriate 
storage  tank. 

In  general,  it  may  be  stated  that  it  is  desirable  to  keep  the 
different  classes  of  solution  as  distinct  as  possible  throughout 
the  whole  series  of  operations;  where  large  volumes  of  slime- 
pulp  have  to  be  rapidly  transferred,  open  wooden  launders  may 
often  be  substituted  for  pipes  with  great  advantage,  both  owing 


HANDLING   OF  SOLUTIONS  239 

to  reduced  friction  and  owing  to  the  opportunity  for  aeration 
which  they  afford. 

The  inside  diameters  of  solution  pipes  vary  from  1  to  4  in., 
according  to  the  rate  of  flow  required  in  the  liquid  passing  through 
them. 

(E)    ARRANGEMENTS  FOR  HEATING  SOLUTIONS 

In  very  cold  climates  it  is  necessary  to  enclose  the  whole  plant 
in  a  suitable  shed  or  building,  warmed  sufficiently  to  prevent  the 
solutions  from  freezing.  In  some  cases  it  has  been  found  that 
higher  extractions  are  obtained  by  the  use  of  hot  solutions,  at  a 
temperature  of,  say,  100°  to  130°  F.,  and  provision  is  sometimes 
made  for  heating  solution  or  slime-pulp  by  the  injection  of  steam. 
According  to  Julian  and  Smart's  experiments,1  the  maximum 
solubility  of  gold  in  cyanide  solutions  of  0.25  per  cent.  KCy  is 
observed  at  a  temperature  of  85°  C.  (185°  F.).  But  as  the  tem- 
perature of  the  solution  also  affects  the  action  of  cyanide  on  other 
constituents  of  the  ore,  heating  the  solution  may  in  some  cases 
be  a  disadvantage.  In  most  cases  it  is  doubtful  whether  the 
improved  extraction  outweighs  the  increased  cost.  Experiments 
made  by  the  writer  in  conjunction  with  Mr.  J.  J.  Johnston  at 
Minas  Prietas,  Mexico,  showed  no  distinct  advantage;  other 
factors  in  the  treatment  seemed  to  be  of  greater  importance,  as 
the  higher  extractions  were  obtained  sometimes  with  cold  and 
sometimes  with  hot  solutions. 

1  Loc.  tit.,  p.  91. 


PART  V 

THE    PRECIPITATION    AND    SMELTING    PROCESSES 

THE  processes  of  precipitation  and  smelting  have  for  their 
object  the  recovery  of  the  gold  and  silver  extracted  by  the 
cyanide  solution  in  a  marketable  form. 

In  the  precipitation  process,  the  precious  metals  are  thrown 
out  of  solution  with  as  little  admixture  of  foreign  impurities  as 
possible  and  obtained  in  the  solid  state,  but  usually  in  a  very 
finely  divided  condition.  In  the  smelting  process,  the  finely 
divided  precipitate  is  brought  by  the  action  of  heat  into  a  coherent 
metallic  mass,  and  impurities  are  removed  as  far  as  practicable 
by  the  use  of  suitable  fluxes  and  reagents.  Many  different  pro- 
cesses of  precipitation  have  been  proposed,  some  of  which  will 
be  described  in  a  subsequent  part  of  this  book;  the  present 
discussion  will  be  confined  to  the  usual  method,  namely,  the 
deposition  of  the  gold  and  silver  on  zinc  shavings  or  filaments. 

The  finely-divided  precipitate  obtained  in  this  process  is 
frequently  referred  to  as  "slimes";  here,  however,  this  term 
will  be  restricted  exclusively  to  its  more  usual  sense,  namely, 
the  finely  divided  and  generally  unleachable  material  obtained 
in  the  crushing  or  grinding  of  ores. 


SECTION  I 

ZINC-BOX  CONSTRUCTION   AND   PRACTICE 

(A)  ZiNc-Box  CONSTRUCTION 

THE  precipitation  by  zinc  shavings  is  carried  out  in  rectangular 
boxes  or  troughs,  divided  by  transverse  partitions  into  a  number 
of  compartments.  The  partitions  are  so  arranged  that  the  solu- 
tion flows  alternately  downward  through  a  narrow  compartment, 
and  upward  through  a  wide  one,  the  latter  alone  containing  the 
zinc  shavings.  The  hight  of  every  alternate  partition  is  one  or  two 
inches  lower  than  that  of  the  succeeding  one,  so  that  the  liquid, 
after  ascending  through  a  wide  compartment,  overflows  the  lower 
partition  into  the  narrow  space  between  it  and  the  next  (higher) 
partition;  the  lower  edge  of  the  latter  is  raised  several  inches 
above  the  floor  of  the  box,  so  that  the  solution  flows  under  it 
into  the  next  wide  compartment,  and  so  on.  (See  Fig.  37.) 

The  dimensions  of  the  boxes  vary,  according  to  the  work 
required  of  them;  the  following  may  be  taken  as  representing 
ordinary  conditions:  Length,  12  to  24  ft.;  width,  1J  to  3  ft.; 
hight,  2i  to  3  ft. 

The  sides,  ends,  and  bottoms  are  usually  constructed  of  IJ-in. 
boards,  strongly  held  together  by  bolts  passing  horizontally  from 
side  to  side  of  the  box,  generally  through  the  narrow  compartments. 
Vertical  bolts  are  also  used  for  securing  the  floor  of  the  box  to  the 
sides.  The  partitions,  which  may  be  of  thinner  boards,  fit  into 
vertical  grooves. 

The  box  is  preferably  raised  somewhat  above  the  floor  of  the 
extractor  house,  and  should  have  a  slight  fall  from  the  feed  to 
the  discharge  end.  Sometimes  the  bottom  is  inclined  to  one  side, 
and  plugs  are  provided  on  this  side  just  above  the  bottom,  so 
that  the  precipitate  may  be  easily  collected  during  the  clean-up. 
The  advantage  of  this  latter  arrangement  is  somewhat  doubtful, 
as  it  may  lead  to  losses  through  leakage,  etc. 

In  each  of  the  wide  compartments  is  a  tray,  resting  loosely 

243 


244 


THE  CYANIDE   HANDBOOK 


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ZINC-BOX  CONSTRUCTION  AND   PRACTICE  245 

on  supports  fastened  to  the  sides  of  the  box.  The  bottom  of 
this  tray  is  formed  of  wire  screening,  generally  with  four  holes  to 
the  linear  inch,  and  serves  to  hold  the  zinc  shavings.  The  sides 
are  of  wood,  with  iron  handles  by  which  the  tray  may  be  lifted 
out  of  the  box  when  necessary.  The  last  compartment,  at  the 
exit  end  of  the  box,  has  an  outlet  near  the  top,  from  which  a 
pipe  leads  either  to  the  storage  tanks  or  to  a  small  sump  whence 
the  precipitated  solution  is  pumped  to  the  storage  tanks. 

Zinc-boxes  of  similar  design  are  also  constructed  of  iron  or 
steel,  painted  or  enameled  so  as  to  resist  the  action  of  cyanide 
or  alkali  solutions.  For  further  details  of  zinc-box  construction, 
see  Julian  and  Smart.1 

(B)  CIRCULAR  VATS  FOR  ZINC  PRECIPITATION 

W.  A.  Caldecott 2  has  advocated  the  use  of  circular  vats  in 
place  of  zinc-boxes  for  precipitation.  The  vat  is  filled  with  zinc 
shavings  resting  on  a  circular  perforated  tray.  The  solution  is 
introduced  from  below  and  ascends  evenly  through  the  mass  of 
shavings.  The  exit  pipe  is  placed  near  the  top  of  the  vat,  and 
extends  to  the  center,  being  bent  upward  at  the  orifice.  The 
advantages  claimed  are  that  the  tendency  to  uneven  flow  ob- 
served in  rectangular  boxes  is  avoided,  that  there  is  less  liability 
to  leakage,  and  that  there  is  economy  of  space  as  compared  with 
ordinary  boxes.  In  the  rectangular  box  there  is  a  likelihood  of 
channels  of  easy  flow  occurring  at  the  sides  and  especially  at  the 
corners  of  the  compartments,  leading  to  imperfect  precipitation, 
unless  great  care  is  exercised  in  packing  the  shavings  into  the 
box. 

A  further  development  of  this  idea  is  due  to  P.  S.  Tavener,3 
who  uses  a  circular  vat  with  a  conical  bottom.  A  stirrer  mounted 
on  a  central  vertical  axis  has  paddles  which  revolve  in  the  space 
beneath  the  perforated  bottom.  At  the  clean-up,  the  precipitate 
which  passes  through  the  screen  may  thus  be  swept  toward  the 
central  discharge  hole.  The  solution  to  be  precipitated  descends 
through  a  central  column  and  ascends  through  the  perforated 
bottom,  passes  through  the  mass  of  zinc  shavings,  and  overflows 
into  a  circular  launder  at  the  top  of  the  vat. 

i "  Cyaniding  Gold  and  Silver  Ores,"  2d  edition,  pp.  306-307. 

2  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  762  (Aug.,  1899). 

3  Julian  and  Smart,  loc.  tit.,  p.  308. 


246  THE  CYANIDE  HANDBOOK 

(C)  CUTTING  AND  PREPARING  THE  ZINC  SHAVINGS 

The  shavings  are  prepared  from  sheet  zinc,  which  is  cut  into 
disks  punched  in  the  middle,  so  that  a  large  number  can  be  set 
side  by  side  on  a  lathe.  While  rapidly  revolving,  a  chisel  is  held 
against  the  edges  of  the  disks.  The  width  and  thickness  of  the 
shavings  can  be  varied  within  certain  limits  by  the  manner  of 
holding  the  cutting  tool,  and  by  altering  the  speed  of  revolution. 

There  is  considerable  difference  of  opinion  as  to  the  best  thick- 
ness for  the  zinc  shavings.  As  effective  precipitation  depends  on 
exposing  a  large  surface  to  the  liquid,  it  would  seem  that  the  sha- 
vings should  be  cut  as  fine  as  possible;  on  the  other  hand  very  fine 
shavings  rapidly  dissolve  or  break  to  pieces,  and  eventually  form 
lumps  which  choke  the  zinc-boxes,  giving  a  precipitate  full  of 
small  pieces  of  zinc  which  is  very  troublesome  to  smelt.  Ordinary 
commercial  zinc  is  preferable  for  this  purpose  to  chemically  pure 
zinc,  owing  to  the  electrical  actions  set  up  by  the  contained  impu- 
rities, but  very  impure  zinc  should  not  be  used,  especially  if  con- 
taining much  arsenic  and  antimony,  as  these  metals  may  give 
rise  to  much  trouble  in  the  subsequent  treatment  of  the  precipi- 
tate. For  effective  work,  the  shavings  should  be  freshly  prepared, 
and  as  free  as  possible  from  oxide. 

(D)  LEAD-ZINC  COUPLE 

In  order  to  increase  the  efficiency  of  the  zinc  for  precipitating, 
it  is  a  very  usual  practice  to  dip  the  shavings,  before  charging 
them  into  boxes,  in  a  1  to  5  per  cent,  solution  of  lead  acetate, 
which  causes  an  immediate  deposit  of  finely-divided  lead  on  the 
surface  of  the  zinc.  This  forms  a  powerful  galvanic  couple,  which 
is  capable  of  depositing  gold  from  solutions  much  weaker  in  free 
cyanide  than  can  be  precipitated  by  the  ordinary  zinc  shavings. 
In  cases  where  much  copper  is  present  in  the  solution,  the  use 
of  zinc-lead  couple  is  often  advantageous.  The  upper  compart- 
ments, in  this  case,  are  filled  with  ordinary  shavings  and  serve  to 
precipitate  gold  and  silver;  in  the  lower  compartments  are  placed 
the  shavings  which  have  been  dipped  in  lead  acetate;  these  pre- 
cipitate copper  much  more  energetically  than  the  plain  zinc 
shavings,  and  so  prevent  this  metal  from  accumulating  in  the 
solution  to  an  injurious  extent.  This  important  improvement  in 
the  zinc  precipitation  process  was  introduced  by  J.  S.  MacArthur 


ZINC-BOX  CONSTRUCTION   AND   PRACTICE  247 

at  the  Lisbon  Berlyn  mine,  Lydenburg,  Transvaal,  about  1894,1 
with  successful  results,  but  does  not  appear  to  have  been  adopted 
elsewhere  until  it  was  brought  forward  at  Johannesburg,  in  1898, 
by  W.  K.  Betty  and  T.  L.  Carter. 

(E)  CHARGING  THE  ZINC  INTO  THE  BOXES 

The  best  results  are  obtained  when  the  zinc  forms  a  homogene- 
ous, spongy  mass.  The  compartments  should  be  well  filled,  but 
the  shavings  should  not  be  pressed  down  too  tightly.  Especial 
care  should  be  taken  in  filling  the  corners,  and  any  parts  where 
it  appears  likely  that  channels  may  form.  The  boxes  should  be 
inspected  from  time  to  time  while  the  solution  is  passing  through 
and  any  irregularities  in  the  flow  rectified  by  adding  fresh  shav- 
ings, if  necessary.  A  plan  sometimes  adopted  is  to  arrange  the 
shavings  in  layers  crossing  each  other  alternately  at  right  angles. 
The  zinc  is  cut  into  very  long  threads,  as  thin  as  possible  without 
becoming  too  brittle;  these  are  laid  in  separate  bundles  on  the 
trays  in  each  compartment;  another  layer  of  bundles  is  placed 
over  these  at  right  angles.  This  arrangement  is  said  to  be  very 
effective  in  preventing  irregular  flow. 

The  quantity  of  zinc  to  be  used  per  cubic  foot  of  space  varies 
considerably,  according  to  the  manner  in  which  it  has  been  cut 
and  other  circumstances.  The  action  of  the  solution  on  the  zinc 
is  naturally  most  active  near  the  head  of  the  box;  as  the  zinc 
dissolves  in  the  top  compartments,  the  shavings  from  the  lower 
compartments  are  taken  out  to  replace  them,  and  fresh  zinc  is 
placed  in  the  lower  compartments. 

The  first  and  last  compartments  of  the  box  are  frequently 
left  empty,  the  first  as  a  safeguard  against  suspended  matter 
which  might  be  carried  through  by  the  solution  and  deposited 
on  the  zinc,  and  the  last  as  a  trap  to  retain  any  fine  precipitate 
which  might  be  carried  over  by  the  flow  of  solution,  especially 
during  the  transfer  of  shavings  from  one  compartment  to  another 
or  during  any  disturbance  of  the  box.  The  last  compartment 
has  occasionally  been  filled  with  coke  or  sawdust,  with  the  object 
of  filtering  out  any  finely  divided  precipitate  which  might  be 
contained  in  the  effluent.  This  compartment  would,  in  the  latter 
case,  only  be  cleaned  up  occasionally,  perhaps  once  in  three 
months,  when  the  filtering  material  would  be  burned  and  the 

i  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  448  (Oct.  1898). 


248  THE  CYANIDE  HANDBOOK 

values  recovered  by  smelting  the  ashes.  Whenever  the  zinc  in 
the  boxes  is  to  be  moved  or  disturbed  in  any  way,  the  flow  of 
solution  should  be  cut  off  or  diverted  to  another  box,  to  avoid 
the  danger  of  suspended  gold  precipitate  being  carried  out  of 
the  boxes  in  the  effluent  solution. 

The  boxes  should  be  "  dressed  "  at  least  twice  a  day,  and  fresh 
zinc  added  as  required.  Careful  attention  to  the  filling  of  the 
zinc-boxes  is  a  very  important  factor  in  the  successful  operation 
of  the  process. 

(F)  CONDITIONS  WHICH  INFLUENCE  PRECIPITATION 

The  principal  conditions  on  which  satisfactory  precipitation 
depends  are:  (1)  the  freedom  of  the  entering  solution  from  solid 
matter  in  suspension;  (2)  the  presence  of  a  sufficient  amount  of 
free  cyanide;  (3)  the  presence  of  sufficient  free  alkali;  (4)  the  ab- 
sence of  excessive  amounts  of  foreign  salts,  particularly  of  copper 
and  iron  compounds;  (5)  a  regular  and  uniform  flow  of  liquid 
through  the  box;  (6)  a  sufficient  volume  of  zinc  per  ton  of  solu- 
tion to  be  precipitated  per  day;  (7)  a  clean,  unoxidized  surface,  on 
which  the  gold  and  silver  are  deposited  in  a  loose  flocculent  con- 
dition, easily  detached. 

Influence  of  Suspended  Matter.  —  The  precautions  usually 
taken  to  prevent  the  entrance  of  suspended  matter  —  sand,  slime, 
organic  substances,  etc.  —  into  the  boxes  have  already  been 
described  (Part  IV,  Section  IV,  B).  When  such  substances  are 
present  they  are  not  only  liable  to  coat  the  zinc  shavings  with 
deposits  of  different  kinds,  thus  interfering  mechanically  with 
the  precipitation  of  the  precious  metals,  but  the  foreign  matter 
thus  introduced  adds  greatly  to  the  expense  and  trouble  of  the 
smelting  operation,  extra  fluxes  being  required  to  remove  it. 
Where  efficient  settling  tanks  or  clarifiers  are  not  provided,  it  is 
customary  to  leave  the  first  wide  compartment  of  the  box  empty 
with  the  object  of  collecting  any  sediment.  In  some  cases  this 
compartment  is  filled  with  coarse  sand,  coir  fiber,  or  other  filter- 
ing medium. 

Influence  of  Free  Cyanide.  —  When  ordinary  zinc  shavings  or 
filaments  are  used  for  precipitation,  it  is  found  that  the  precipita- 
tion of  gold  and  silver  is  very  much  more  effective  in  solutions 
carrying  a  fair  amount  of  free  cyanide  than  in  solutions  weak 
in  cyanide.  The  strength  of  the  entering  solution  should  never 


ZINC-BOX  CONSTRUCTION  AND   PRACTICE  249 

be  allowed  to  fall  much  below  0.2  per  cent.  KCN,  and  in  some 
cases  it  is  advantageous  to  allow  a  strong  solution  to  drip  slowly 
into  the  top  compartment  of  the  box,  to  ensure  a  sufficient  strength 
for  good  precipitation.  When  the  zinc-lead  couple  is  used  the 
matter  is  of  less  consequence  and  very  weak  solutions  can  in  gen- 
eral be  precipitated  by  it.  T.  L.  Carter l  found  that  solutions  of 
0.005  to  0.008  per  cent,  free  cyanide  could  be  satisfactorily  pre- 
cipitated, with  an  extraction  of  90  to  95  per  cent,  of  the  gold, 
using  the  zinc-lead  couple  and  a  drip  of  strong  cyanide  at  the 
head  of  the  box,  so  that  at  the  beginning  the  strength  of  the 
entering  solution  was  raised  to  0.025  per  cent. ;  after  12  or  14  hours 
the  strength  was  allowed  to  fall  to  0.008  per  cent.  Other  workers 
using  the  lead-zinc  couple  have  found  the  strong  cyanide  drip 
quite  unnecessary.  Occasionally  a  drip  of  lead  acetate  solution 
is  used. 

It  would  appear  that  the  presence  of  some  other  salts  besides 
cyanide  may  in  certain  cases  induce  good  precipitation  of  gold  on 
zinc,  for  it  has  been  observed  that  solutions  which  have  become 
very  "foul,"  that  is,  highly  charged,  with  accumulated  salts, 
chiefly  complex  cyanogen  compounds  of  iron,  zinc,  copper,  etc., 
sometimes  precipitate  their  gold  contents  on  clean  zinc  better 
than  solutions  otherwise  pure,  but  weak  in  free  cyanide,2  and 
it  is  even  possible  to  precipitate  in  the  complete  absence  of  free 
cyanide.  Another  advantage  of  a  sufficient  strength  in  free 
cyanide  is  that  the  formation  of  injurious  deposits  in  the  boxes 
is  largely  prevented.  The  so-called  "white  precipitate"  con- 
sisting of  hydrate,  cyanide,  and  ferrocyanide  of  zinc,  chiefly  occurs 
in  boxes  where  weak  solutions  are  precipitated.  Strong  cyanide 
solutions  also  are  less  liable  to  precipitate  copper  in  preference  to 
gold. 

Influence  of  Alkali.  —  A  certain  minimum  of  free  alkali  is 
found  to  be  essential  for  good  precipitation.  On  the  other  hand, 
a  large  excess  should  be  avoided.  Whether  alkalies  actually 
decompose  the  double  cyanides  of  zinc  with  liberation  of  free 
cyanide  appears  somewhat  doubtful,  but  their  presence  undoubt- 
edly increases  the  solvent  efficiency  of  these  compounds,  and  also 
promotes  precipitation.  They  are  also  solvents  for  some  at  least 
of  the  constituents  in  the  white  precipitate  referred  to  above. 

1  "  Proc.  Chera.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  440. 

2  Alfred  James,  "  Trans.  A.  I.  M.  E.,"  XXVII,  278. 


250  THE  CYANIDE   HANDBOOK 

Excessive  amounts  of  alkali  cause  a  violent  action  on  the  zinc, 
with  great  waste  of  the  metal,  accompanied  by  "foaming,"  due 
to  the  evolution  of  large  quantities  of  hydrogen,  and  a  tendency  for 
the  gold  precipitate  to  be  detached  and  carried  away  by  the  flow 
of  solution.  Too  large  a  quantity  of  lime  in  solution  may  lead 
to  the  deposition  of  insoluble  calcium  compounds,  carbonate  or 
sulphate,  on  the  surface  of  the  zinc,  owing  to  reactions  between 
the  lime  and  the  soluble  carbonates  and  sulphates  present  as 
impurities  in  the  cyanide  or  extracted  from  the  ore.  During  the 
passage  of  solution  through  the  boxes  an  increase  of  alkalinity 
is  invariably  observed.  This  is  explained  in  the  section  dealing 
with  the  chemistry  of  the  process. 

It  is  occasionally  found  necessary  to  add  alkali,  either  in  the 
zinc-boxes  themselves  or  in  the  storage  tanks.  In  some  cases 
addition  of  sodium  carbonate  to  the  solution  in  the  sumps  has  a 
beneficial  effect,  as  it  precipitates  salts  which  might  otherwise 
cause  a  deposit  of  insoluble  carbonates  in  the  boxes. 

Rate  of  Flow.  —  Under  a  given  set  of  conditions  the  slower 
the  rate  of  flow  the  more  complete  will  be  the  precipitation.  It 
is  found,  however,  that  an  increased  rate  of  flow  may  be  com- 
pensated for  by  increasing  the  surface  of  zinc  with  which  the 
solution  must  come  in  contact;  and  as  a  rapid  flow  has  other 
advantages,  it  is  generally  good  practice  to  pass  the  solution 
through  the  boxes  as  rapidly  as  is  consistent  with  efficient  pre- 
cipitation. 

In  the  early  days  of  the  process  it  was  considered  necessary 
to  use  about  f  cu.  ft.  of  zinc  shavings  to  precipitate  the  solutions 
used  in  treating  each  ton  of  ore  per  day;  1  according  to  modern 
practice,  as  much  as  7  or  even  12  tons  of  solution  can  be  precipi- 
tated per  cubic  foot  of  zinc  per  day.2  The  actual  rate  of  flow  in 
the  latter  case  may  be  from  7  to  13  cu.  ft.  per  minute  across  a 
section  of  14  sq.  ft.  of  zinc,  or  0.5  to  0.92  ft.  per  minute  for  each 
square  foot  of  section.  This  method,  however,  can  only  give 
good  results  when  much  care  is  taken  in  charging  the  compart- 
ments. 

According  to  Caldecott  and  Johnson,3  a  pound  of  ordinary 
zinc  shavings  exposes  about  40  sq.  ft.  of  surface;  a  cubic  foot  of 

•  W.  H.  Gaze,  "  Handbook  of  Practical  Cyanide  Operations"  (1898). 
2  Julian  and  Smart,  loc.  cit.,  p.  142. 

3"Proc.  Chem.,  Met.  Min.  Soc.  of  South  Africa,"  IV,  263.  See  also  Gaze, 
loc.  cit. 


ZINC-BOX  CONSTRUCTION   AND   PRACTICE  251 

the  shavings,  as  usually  packed  in  the  compartments,  would  weigh 
from  3.5  to  4  lb.,  and  hence  exposes  a  precipitating  surface  of 
140  to  160  sq.  ft.  Taking  the  volume  of  a  ton  of  solution  as  32 
cu.  ft.  (Part  IV,  Section  IV),  a  zinc-box  of  8  compartments, 
each  containing  4  cu.  ft.  actually  occupied  by  zinc  shavings, 
would  contain  at  any  moment  1  ton  of  solution  undergoing  pre- 
cipitation and  exposed  to  a  precipitating  surface  of  about  4800 
sq.  ft.  If  1  ton  of  solution  be  precipitated  per  cu.  ft.  per  day, 
32  tons  of  solution  must  pass  through  the  box  per  day;  in  other 
words,  the  rate  of  flow  will  be  1  ton  in  45  minutes. 

Nature  of  the  Precipitating  Surface.  —  It  has  already  been 
pointed  out  that  the  best  results  are  usually  attained  by  cutting 
the  zinc  in  very  long,  thin  threads.  These  usually  have  a  thick- 
ness of  5^  to  T^QO  in.,  and  a  width  of  TV  to  J  in.,  but  practice 
varies  very  widely  in  these  particulars.  The  smaller  surface  ex- 
posed by  thick  shavings  may  be  largely  compensated  for  by  using 
the  lead-zinc  couple  and  thus  obtaining  greater  precipitating 
efficiency.  Mixtures  of  lead  and  zinc  shavings,  and  shavings  pre- 
pared from  an  alloy  of  zinc  containing  3  per  cent,  of  lead,  have 
also  been  used,  and  are  more  effective,  especially  with  solutions 
weak  in  cyanide,  than  ordinary  zinc  shavings.  These  combi- 
nations, however,  are  less  generally  adopted  and  probably  less 
energetic  than  the  couple  formed  by  immersing  the  zinc  in  a 
solution  of  a  lead,  salt. 

Zinc-copper  and  zinc-mercury  couples  have  also  been  tried, 
and  are  as  efficient  as  the  zinc-lead  couple  in  promoting  precipita- 
tion of  gold  and  silver;  but  they  have  certain  serious  drawbacks. 
Mercury  causes  the  shavings  to  fall  to  pieces  and  rapidly  reduces 
them  to  a  pulpy  mass,  from  which  the  mercury  may  be  separated 
by  squeezing  through  a  cloth.1  When  copper  is  used  for  this 
purpose,  a  very  base  bullion  is  obtained  in  the  smelting  of  the 
precipitate. 

Great  care  must  be  taken  to  expose  the  shavings  to  the  at- 
mosphere as  little  as  possible.  When  charged  into  the  boxes, 
they  should  be  freshly  turned,  clean  and  unoxidized;  the  com- 
partments should  be  filled  so  that  about  an  inch  of  solution  is 
left  over  the  top  of  the  zinc,  and  the  moist  shavings  especially 
should  never  be  exposed  to  the  air  any  longer  than  absolutely 
necessary  during  transfer  from  one  compartment  to  another. 

i  W.  H.  Virgoe,  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  IV,  615. 


252  THE  CYANIDE  HANDBOOK 

It  may  generally  be  assumed  that  satisfactory  precipitation 
is  taking  place  when  the  deposit  of  gold  and  silver  is  in  a  loose 
condition  and  of  a  brownish-black  color.  When  a  smooth,  co- 
herent, metallic  deposit  is  observed,  the  precipitation  soon  ceases 
altogether,  and  it  is  probable  that  some  alteration  is  necessary 
in  the  conditions. 

A  vigorous,  but  not  too  violent,  evolution  of  hydrogen  also 
accompanies  good  precipitation;  the  reduction  of  the  gold-alkali 
cyanide  and  consequent  precipitation  of  the  gold  is  commonly 
supposed  to  be  due  to  nascent  hydrogen,  that  is,  to  an  action 
taking  place  between  the  gold  compound  and  the  hydrogen  at 
the  moment  when  the  latter  is  set  free  by  the  decomposition  of 
water,  as  explained  in  Part  II.  On  the  other  hand,  the  accumula- 
tion of  bubbles  of  hydrogen  on  the  surface  of  the  zinc  hinders 
precipitation.  The  gas  in  this  form  has  no  action  whatever  on 
the  gold  compound,  and  prevents  contact  between  the  solution 
and  the  zinc  surface.  Hence  the  occasional  removal  of  the 
bubbles  by  shaking  or  turning  over  the  zinc  shavings  tends  to 
promote  good  precipitation. 

(G)  DIFFICULTIES  IN  ZINC  PRECIPITATION 

These  difficulties  have  already  been  alluded  to  in  discussing 
the  conditions  which  influence  precipitation;  it  may,  however,  be 
of  advantage  to  recapitulate  them.  They  are:  (1)  Deposition  of 
suspended  matter  on  the  surface  of  the  shavings.  (2)  Formation 
of  insoluble  compounds  coating  the  shavings,  by  chemical  action  of 
cyanide,  alkali,  or  other  substances  on  the  zinc.  (3)  Formation 
of  insoluble  compounds  by  subsidiary  actions  going  on  between 
various  substances  in  the  solution  passing  through  the  boxes. 
(4)  Formation  of  thin  metallic  coatings  (of  gold,  silver,  copper, 
etc.),  which  protect  the  zinc  from  the  solution  and  so  check 
further  precipitation.  (5)  "  Polarization  "  of  the  zinc,  by  accumu- 
lation of  hydrogen  bubbles  on  its  surface.  (6)  Imperfect  depo- 
sition of  gold  and  silver  from  solutions  not  sufficiently  strong  in 
cyanide.  (7)  Excessive  consumption  of  zinc  under  certain  con- 
ditions. (8)  Irregularities  of  flow  due  to  the  formation  of  channels, 
thus  leading  to  inefficient  precipitation. 

Deposits  Formed  by  Action  of  Solution  on  Zinc.  —  These  are 
generally  due  to  insufficiency  of  free  cyanide.  Researches  on 
the  nature  of  these  deposits  have  shown  that  they  generally 


ZINC-BOX  CONSTRUCTION  AND   PRACTICE  253 

consist  principally  of  hydrated  zinc  oxide,1  presumably  formed 
by  the  oxygen  liberated  in  the  electrolysis  of  water  by  the  various 
metallic  couples  present  in  the  box,  in  which  the  zinc  acts  as 
anode.  Relatively  small  quantities  of  zinc  cyanide  may  also  be 
present.  As  these  compounds  are  soluble  in  a  sufficiently  strong 
cyanide  solution,  the  obvious  remedy  is  to  increase  the  strength 
of  the  solution  entering  the  box  by  addition  of  cyanide,  but  this 
is  not  always  practicable.  When  large  quantities  of  iron  are 
dissolved  from  the  ore  as  ferrocyanides,  there  may  be  a  precipita- 
tion in  the  boxes  of  ferrocyanide  of  zinc,  or  of  some  insoluble 
double  ferrocyanide  of  zinc  and  an  alkali  metal.  These  deposits 
are  still  more  troublesome  as  they  do  not  readily  redissolve, 
either  in  cyanide  or  alkali.  In  many  cases  the  only  remedy  is, 
after  the  deposit  has  accumulated  to  a  certain  extent,  to  clean 
up  the  box  and  start  afresh  with  clean  zinc.  Ammonium  salts 
and  sodium  chloride  have  sometimes  been  added  as  solvents  for 
deposits  of  insoluble  zinc  compounds. 

Caldecott  and  Johnson  (loc.  cit.)  appear  to  consider  that  a 
mixture  of  lead  and  zinc  shavings  is  preferable  to  the  lead-zinc 
couple  in  cases  where  deposition  of  zinc  hydrate  takes  place;  they 
state  that  "a  mixture  of  lead  and  zinc  shavings  has  a  lengthy 
efficiency,  possibly  due  to  the  fact  that  the  zinc  hydrate  does  not 
coat  the  whole  couple  to  the  same  extent  as  with  the  usual  lead- 
coated  zinc  shavings." 

Other  Deposits  Due  to  Subsidiary  Reactions.  —  The  deposition 
of  calcium  carbonate  and  sulphate  in  the  boxes  has  already  been 
mentioned.  Under  certain  conditions  alumina,  and  possibly 
silica  from  soluble  silicates,  may  separate  out.  Solutions  con- 
taining manganese  very  readily  throw  down  a  brown  hydrated 
oxide  of  the  metal. 

Sulphur,  either  as  finely  divided  pyrites  carried  through 
mechanically  and  settling  on  the  shavings,  or  as  sulphide  of  zinc 
due  to  the  reaction  between  zinc  hydrate  and  alkaline  thiocyanates 
in  the  solution,  is  also  frequently  present,  and  when  iron  or  other 
base  metal  is  contained  in  the  precipitate  may  give  rise  to  the 
formation  of  a  matte  during  the  smelting. 

At  Redjang  Lebong,  Sumatra,  selenium  is  precipitated  in 
the  zinc-boxes  in  considerable  quantity,  but  no  evidence  is  at 
hand  as  to  the  form  in  which  it  occurs.  It  is  particularly  trouble- 

i  "  Journ.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa  "  V,  62,  75. 


254  THE  CYANIDE  HANDBOOK 

some,  as  it  is  extremely  difficult  to  eliminate  it  completely  in  the 
subsequent  operations,  and  its  presence  in  the  bullion  even  in 
small  quantities  is  very  detrimental,  as  it  renders  it  brittle. 

Arsenic,  antimony,  lead,  and  mercury,  if  present  in  solution, 
will  also  be  deposited  on  the  zinc.  Tellurium  probably  acts 
similarly  to  sulphur  and  selenium. 

"  Metallic  "  Coatings.  —  As  already  pointed  out,  gold  is  some- 
times deposited,  not  in  a  loose  flocculent  condition,  but  as  a  bright 
metallic  coating  having  the  natural  color  of  gold.  This  occurs 
chiefly  when  the  solutions  are  either  very  rich  in  gold,  or  low  in 
cyanide.  There  are  considerable  grounds,  as  pointed  out  by 
Argall,  for  supposing  that  the  ordinary  loose  precipitate  is  a  com- 
pound of  zinc,  gold,  and  cyanogen,  while  the  metallic  coating 
referred  to  above  is  probably  gold  in  the  elementary  state.  Similar 
metallic  coatings  may  be  formed  with  silver,  copper,  and  mer- 
cury, and  when  they  occur,  further  precipitation  in  those  parts 
of  the  box  in  which  they  are  formed  is  almost  entirely  arrested. 
It  has  been  found  that  the  activity  of  the  coated  shavings  can 
be  restored  by  immersing  them  for  a  few  moments  in  dilute 
sulphuric  acid,  washing  in  water,  and  at  once  replacing  in  the 
boxes. 

Consumption  of  Zinc.  —  The  normal  consumption  of  zinc  on  a 
cyanide  plant  is  from  0.25  to  0.5  Ib.  per  ton  of  ore  treated,  but 
in  special  cases  it  may  be  considerably  more  or  less  than  these 
amounts.  Only  a  portion  of  this  is  actually  dissolved  by  the 
solution,  and  of  that  which  is  dissolved,  only  a  small  part  corre- 
sponds with  the  gold  or  silver  precipitated.  A  large  part  goes  in 
the  form  of  small  fragments  of  metallic  zinc  into  the  precipitate 
collected  during  the  clean-up,  and  a  further  quantity  is  dissolved 
by  subsidiary  reactions  with  cyanide,  alkali,  or  oxygen  from  de- 
composition of  water,  as  already  described.  We  may  thus  dis- 
tinguish two  sources  of  consumption,  mechanical  and  chemical, 
the  former  including  all  zinc  passing  in  a  solid  form  into  the 
precipitate,  and  the  latter  all  that  goes  into  solution.  When  strong 
cyanide  solutions  are  used  the  chemical  loss  is  greater,  but  the 
mechanical  loss  is  less  than  with  weak  cyanide  solution. 

The  following  particulars,  given  by  W.  H.  Virgoe  *  with  regard 
to  two  Mexican  plants,  treating  sand  and  slime  respectively,  are 
of  interest  in  this  connection. 

i  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  IV,  615. 


ZINC-BOX  CONSTRUCTION  AND   PRACTICE  255 

Sand  Plant  Slime  Plant 

Number  of  zinc-boxes     4  4 

Number  of  compartments  per  box 8  5 

Total  zinc  capacity  in  cu.  ft 40.64  60 

Weight  of  zinc  per  cu.  ft.  (Ib.)    13.5  13.5 

Total  zinc  capacity  (Ib) 584.64  810 

Zinc-space  per  ton  of  solution  per  hour  (cu.  ft.)    .  .  25.4  20 

Total  consumption  of  zinc  per  ton  (Ib.) 1.144             1.166 

Mechanical  loss  of  zinc  (per  cent.)    13.9  63.2 

Chemical  loss  of  zinc  (per  cent.)     86.1  36.8 

Tonnage  treated  in  4  months    2646.4  1481 

Consumption  of  cyanide  per  ton  (Ib.) 1.5  0.6 

Strength  of  entering  solution  (per  cent.  KCy)    ....  0.32  0.04 

The  curious  feature  of  these  results  is  that  the  total  consump- 
tion of  zinc  per  ton  of  ore  treated  was  practically  the  same  in 
both  plants,  but  the  nature  of  the  loss  was  entirely  different, 
being  chiefly  chemical  in  the  case  of  the  sand  plant,  where  strong 
solution  was  used,  and  chiefly  mechanical  in  the  slime  plant, 
where  the  solution  entering  was  very  weak  in  cyanide.  In  the 
latter  case  the  gold  was  no  doubt  largely  deposited  as  a  thin  film 
which  could  not  be  detached  from  the  shavings  by  slight  rubbing, 
so  that  a  large  quantity  of  metallic  zinc  had  to  be  smelted  in  order 
to  recover  the  values. 

Estimating  the  consumption  of  zinc  merely  by  the  amount 
used  up  per  ton  of  ore  treated  may  give  a  false  idea  of  the  work 
actually  done  by  the  boxes;  a  more  exact  gauge  of  efficiency  is 
often  obtained  by  considering  the  amount  of  zinc  consumed  per 
ton  of  solution  passed  through,  or  per  ounce  of  gold  or  silver 
precipitated.  On  the  latter  basis,  the  efficiency  of  zinc  for  pre- 
cipitating silver  is  generally  much  greater  than  for  gold,  chiefly 
because  the  entering  solutions  carry  a  much  larger  percentage 
by  weight  of  precious  metal.  Heavy  mechanical  losses  of  zinc 
are  generally  due  to  errors  either  in  the  preparation  of  the 
shavings,  or  in  the  handling  of  them  during  the  passage  of  solution 
or  during  the  clean-up.  Badly  cut  shavings  are  apt  to  give  large 
quantities  of  small  fragments,  which  pass  into  the  precipitate, 
and  many  causes,  such  as  uneven  flow  resulting  in  channels, 
exposure  to  atmosphere,  and  unnecessary  handling,  tend  to  make 
the  zinc  brittle.  The  deposition  of  gold,  etc.,  in  a  thin  coherent 
film  is  also,  as  pointed  out  above,  a  cause  of  mechanical  loss. 

The  causes  of  chemical  loss  have  already  been  fully  discussed. 
It  has  been  considered  that  losses  may  occur  through  contact  of 
zinc  with  iron  surfaces,  as  for  example  in  the  screens  used  to 
support  the  shavings  in  the  compartments.  This,  however,  is 


256  THE  CYANIDE   HANDBOOK 

practically  unavoidable,  and  it  does  not  appear  probable  that 
the  loss  from  this  cause  is  serious,  since  the  iron  rapidly  becomes 
coated  with  a  film  of  oxide  or  carbonate  that  acts  as  an  insulator. 
Precautions  against  Theft.  —  It  is  customary  to  cover  the  tops 
of  the  zinc-boxes  with  wire  screening,  or  with  locked  lids,  which 
are  only  opened  when  it  is  necessary  to  transfer  shavings  or  dur- 
ing the  clean-up  and  refilling  of  the  boxes.  In  many  plants  the 
precipitation  and  smelting  departments  are  strictly  isolated  from 
the  rest  of  the  establishment,  and  only  those  directly  concerned 
are  admitted. 

(H)    NON-ACCUMULATION    OF    ZlNC   IN   THE    SOLUTIONS 

It  is  a  remarkable  fact  that  although  zinc  is  constantly  dis- 
solving during  the  passage  of  the  solution  through  the  boxes,  the 
average  amount  of  it  in  the  solution  remains  about  stationary 
after  it  has  once  reached  a  certain  point.  It  is  evident,  there- 
fore, that  somehow  zinc  is  being  removed  from  the  solution. 
The  amount  of  solution  thrown  away  in  the  residues  and  replaced 
by  fresh  water  does  not  afford  a  sufficient  explanation.  Some 
portion  is  no  doubt  redeposited  in  the  boxes  as  insoluble  zinc 
hydrate,  etc.,  from  solutions  weak  in  cyanide;  some  may  be  pre- 
cipitated in  the  ore  or  in  the  boxes  as  zinc  sulphide,  by  soluble 
sulphides.  Soluble  sulphides  of  the  alkali  metals  may  be  present 
in  commercial  cyanide,  formed  by  the  action  of  alkali  on  sulphides 
in  the  ore,  or  formed  by  reduction  in  the  zinc-boxes  through  the 
action  of  nascent  hydrogen  on  the  thiocyanates,  which  are  almost 
invariably  present  in  the  solutions  when  the  ore  under  treatment 
contains  pyrites.  W.  H.  Virgoe  1  has  suggested  that  in  presence 
of  lime  and  carbonic  acid  there  may  be  a  precipitation  of  double 
carbonate  of  zinc  and  calcium,  as  follows: 

K2Zri(CN)4  +  2Ca(OH)2  +  2CO>  =  ZnCa(CO3)2  +  Ca(CN)2  4  2KCN  + 

2H2O. 

(I)  TESTS  FOR  REGULATING  THE  WORKING  OF  THE  BOXES 

The  methods  used  in  making  these  tests  will  be  fully  described 
in  a  later  section  of  this  book.  Samples  of  the  solutions  entering 
and  leaving  the  boxes  should  be  taken  at  frequent  intervals. 
This  is  generally  done  by  means  of  glass  tubes  provided  with 

i  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  IV,  636. 


ZINC-BOX  CONSTRUCTION  AND   PRACTICE  257 

cocks  and  passing  through  the  top  and  bottom  ends  of  the  boxes. 
The  cock  is  turned  so  as  to  allow  a  small  uniform  drip  of  solution, 
which  is  caught  in  a  bottle  beneath.  These  samples  are  tested 
at  regular  intervals,  say  every  12  or  24  hours,  for  cyanide,  alkali, 
and  gold  (for  silver  also  where  this  metal  is  of  importance). 
These  represent  the  average  results  for  equal  periods  of  time. 
Special  samples  for  cyanide  and  alkali  are  generally  required  at 
more  •  frequent  intervals  for  regulating  the  leaching  operations, 
the  supply  of  cyanide  for  the  storage  tanks,  etc.,  and  a  test  is 
commonly  made  of  each  solution  run  on  and  drawn  off  from  each 
charge  under  treatment,  unless  the  material  is  so  uniform  and  the 
conditions  so  regular  as  to  render  this  unnecessary. 

The  strength  of  cyanide  to  be  maintained  depends  on  such 
a  variety  of  circumstances  that  no  general  rule  can  be  given. 
Some  information  on  this  head  will  be  found  in  Part  IV,  Section  I. 

The  alkalinity  needed  also  depends  to  a  certain  extent  on  the 
nature  of  the  material  under  treatment.  A  slight  but  constant 
alkalinity  should  be  maintained  in  the  entering  solution,  this 
being  secured  by  the  addition  of  suitable  amounts  of  lime  to  the 
ore  or  pulp  to  be  treated,  or,  occasionally,  by  the  addition  of 
caustic  soda  to  the  solutions  themselves.  For  slimes  plant  solu- 
tions, W.  A.  Caldecott  recommends  an  alkali  strength  equivalent 
to  0.006  to  0.01  per  cent.  NaOH,1  but  frequently  as  much  as  0.05 
per  cent,  or  more  is  admissible. 

i  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  101. 


SECTION   II 

CLEAN-UP   OF   ZINC-BOXES 
(A)   PRELIMINARY  OPERATIONS 

THE  frequency  of  the  clean-up  will  depend  on  the  nature  and 
amount  of  the  precipitate  which  is  formed.  In  large  plants  it 
may  take  place  once  a  week,  in  small  ones  once  a  month,  the  com- 
mon practice  being  twice  or  three  times  a  month.  When  much 
white  precipitate  has  formed,  it  may  be  necessary  to  clean  up 
oftener  than  would  be  the  case  with  a  clean  gold  deposit  contain- 
ing the  same  values.  Before  cleaning  up  it  is  usual  to  displace 
the  solution  in  the  box  with  water,  to  which  alum  may  be  added 
to  promote  settlement  of  the  precipitate  during  the  process.  In 
some  cases  the  strength  of  the  entering  solution  is  raised  con- 
siderably for  an  hour  or  so  before  it  is  displaced  with  water.  This 
is  for  the  purpose  of  loosening  the  deposit  which  adheres  to  the 
zinc.  After  all  cyanide  has  been  displaced,  a  little  acid  may  be 
added,  which  also  assists  settlement. 

(B)  SEPARATION  OF  PRECIPITATE  FROM  COARSE  ZINC 

The  trays  are  first  lifted  in  the  compartments,  and  shaken  up 
and  down  to  allow  as  much  of  the  precipitate  as  possible  to  pass 
through  the  screen.  The  operator,  wearing  rubber  gloves,  gen- 
erally also  shakes  the  shavings  under  water  in  the  compartment, 
and  then  holds  them  over  an  adjoining  (lower)  compartment  where 
they  are  sprayed  with  a  jet  of  water.  In  some  cases  the  tray  and 
contents  are  lifted  bodily  from  the  box  and  placed  over  the  clean- 
up tank,  into  which  the  fine  adhering  precipitate  is  washed.  The 
washed  shavings  are  then  either  set  aside  in  any  suitable  water- 
tight vessels,  such  as  enameled-iron  pans,  buckets  or  trays,  or 
are  transferred  to  the  lower  compartments  of  another  zinc-box. 
Each  compartment  in  succession  is  treated  in  this  manner,  be- 
ginning at  the  head  and  proceeding  'to  the  foot  of  the  box. 

258 


CLEAN-UP   OF  ZINC-BOXES  259 

(C)  REMOVAL  OF  PRECIPITATE  FROM  Box 

After  the  whole  of  the  coarse  zinc  has  been  lifted  out,  the 
trays  are  turned  over,  washed  and  scrubbed  to  detach  any  adher- 
ing precipitate. 

The  liquid  and  precipitate  remaining  in  the  box  are  then  trans- 
ferred to  a  special  settling  tank,  usually  about  4  ft.  diameter  by 
3  ft.  deep,  known  as  the  clean-up  tank.  This  is  generally  of  wood, 
sometimes  lined  with  lead.  As  this  tank  is  often  used  for  the 
subsequent  acid  treatment  of  the  precipitate,  it  is  sometimes 
provided  with  a  wooden  paddle  mounted  on  a  central  vertical 
shaft,  or  with  other  means  of  stirring.  When  there  are  no  out- 
lets to  the  compartments,  the  transfer  is  made  by  means  of 
enameled-iron  buckets.  In  some  plants,  the  contents  of  the 
box  are  allowed  to  stand  and  settle  for  some  time,  and  the  clear 
liquid  syphoned  off.  The  residue  is  then  scooped  out  and  carried 
to  the  clean-up  tank.  When  plugs  are  provided  at  the  bottom 
of  the  compartments,  these  are  pulled  out  and  the  liquid  allowed 
to  run  into  a  launder  beneath,  which  leads  to  the  clean-up  tank. 
The  sides  of  the  compartments  are  then  washed  down  with  a  hose 
until  the  whole  of  the  precipitate  has  been  cleaned  out  and  run 
into  the  tank.  When  the  box  is  perfectly  clean,  the  coarse  zinc 
is  replaced  on  the  trays  in  the  same  order,  unless  it  has  been 
already  transferred  to  another  box.  The  box  is  at  once  filled  up 
with  solution,  so  as  to  avoid  oxidation  of  the  zinc,  and  is  ready 
for  use  after  any  fresh  zinc  that  may  be  necessary  has  been  added. 

In  some  modern  plants,  the  whole  of  the  liquid  drawn  off 
during  the  clean-up  is  passed  through  a  small  filter-press.  The 
precipitate,  after  passing  through  a  fine  screen  (60-  to  80-mesh), 
is  also  filter-pressed,  and  the  material  retained  on  the  screen 
treated  separately.  Formerly  the  fine  precipitate  was  squeezed 
by  hand  through  filter-bags. 

(D)  SETTLEMENT  AND  SIFTING  OF  PRECIPITATE 

Where  filter-presses  are  not  used,  the  liquid  is  allowed  to 
stand  for  24  to  48  hours  in  the  clean-up  tank,  sometimes  with 
addition  of  a  little  alum,  until  the  precipitate  has  completely 
settled.  The  clear  liquid  is  then  carefully  syphoned  off  and  run 
to  waste.  The  precipitate  during  transfer  to  the  settling  tank 
is  frequently  run  through  a  fine  sieve,  40-  to  80-mesh,  and  any 


260  THE  CYANIDE  HANDBOOK 

material  retained  on  the  sieve  (generally  known  as  "shorts"  or 
"metallics")  is  set  aside  for  separate  treatment.  When  suffi- 
ciently coarse,  it  may  be  returned  to  the  top  compartment  of 
the  box  and  placed  on  a  layer  of  clean  shavings;  if  there  is  too 
much  of  this  product,  however,  or  if  it  is  too  fine,  it  would  be  liable 
to  choke  the  screens  of  the  boxes,  and  it  is  usually  treated  with 
acid  to  dissolve  as  much  as  possible  of  the  zinc,  as  described 
below. 

If  acid  treatment  is  not  to  be  used,  the  settled  precipitate, 
if  free  from  shorts,  may  be  at  once  pumped  to  a  filter-press. 
Lead-lined  tanks  should  not  be  used  when  the  precipitate,  as  is 
often  the  case,  contains  mercury,  as  this  metal  amalgamates 
with  the  lead  and  rapidly  corrodes  the  lining. 

In  some  plants  vacuum  filters  are  used.  As  the  precipitate 
is  very  finely  divided,  the  filtering  medium  must  be  very  closely 
woven,  such  as  flannel  or  very  thick  canvas.  The  liquid  is  drawn 
off  by  a  suction  pump  and  a  wash  of  fresh  water  added,  and  this 
is  again  sucked  through  to  extract  as  much  as  possible  of  any 
soluble  matter  which  may  be  present.  Any  wash-waters  drawn 
off  in  the  above  processes  should  be  assayed  before  finally  running 
to  waste,  as  they  occasionally  carry  sufficient  values  to  be  worth 
recovering.  In  that  case  they  should  be  returned  to  the  boxes, 
after  addition  of  alkali,  if  necessary. 


SECTION  III 
ACID.  TREATMENT   AND    ROASTING    OF    PRECIPITATE 

AFTER  the  precipitate  has  been  separated  as  far  as  possible 
from  the  coarse  zinc,  there  is  considerable  divergence  in  the  sub- 
sequent procedure. 

The  methods  adopted  may  be  briefly  classified  as  follows: 
(1)  Direct  fusion.  (2)  Roasting  and  fusion.  (3)  Mixing  with  niter, 
roasting  and  fusion.  (4)  Acid  treatment  and  fusion.  (5)  Acid 
treatment,  roasting,  and  fusion.  (6)  Roasting,  acid  treatment, 
and  fusion.  (7)  Smelting  with  litharge  and  cupellation.  Since 
acid  treatment  generally  precedes  roasting,  the  operations  will  be 
considered  in  that  order. 

(A)  ACID  TREATMENT 

The  precipitate,  having  been  transferred  to  the  acid  tank 
with  or  without  filtering,  is  allowed  to  settle  somewhat,  and  as 
much  as  possible  of  the  clear  liquid  drawn  off.  Sulphuric  acid 
is  then  added,  in  quantity  more  than  sufficient  to  dissolve  the 
zinc  supposed  to  be  present,  and  diluted  with  enough  water  to 
form  a  10  per  cent,  solution.  The  heat  produced  by  the  mixture 
of  acid  and  water,  with  that  generated  by  the  chemical  action 
of  the  acid  on  the  zinc,  is  generally  sufficient  to  maintain  the  re- 
action with  sufficient  vigor  till  the  greater  part  of  the  zinc  is  dis- 
solved. In  some  cases  it  may  be  necessary  to  apply  artificial 
heat,  by  injection  of  steam  or  otherwise.  The  mixture  is  stirred 
from  time  to  time,  mechanically  or  by  hand. 

At  first  there  is  a  very  violent  disengagement  of  gases,  chiefly 
hydrogen,  but  mixed  also  with  hydrocyanic  acid  and,  where  arsenic 
is  present,  with  arseniureted  hydrogen.  As  the  latter  are  ex- 
tremely poisonous,  it  is  necessary  to  provide  a  hood  with  a  good 
draft,  for  carrying  off  the  fumes.  The  tank  must  be  sufficiently 
large  to  avoid  the  danger  of  frothing  over.  When  all  action  has 

261 


262  THE  CYANIDE  HANDBOOK 

ceased,  the  tank  is  filled  up  with  water,  preferably  hot,  as  the  zinc 
sulphate  formed  is  more  soluble  in  hot  water.  The  mixture  is 
stirred,  allowed  to  settle,  and  the  clear  liquid  drawn  off,  this 
operation  being  repeated  several  times.  The  acid  tank  may  be 
of  wood,  with  or  without  a  lead  lining,  or  of  enameled  iron. 

Sodium  bisulphate  (a  by-product  in  the  manufacture  of  nitric 
acid)  is  sometimes  used  as  a  substitute  for  sulphuric  acid.  An 
8  per  cent,  solution  of  the  salt  is  an  effective  strength.  The  tem- 
perature should  not  be  above  33°  C.,  as  the  solubility  of  the  salt 
decreases  with  rise  of  temperature.1  This  material  is  cheaper 
and  more  easily  transported  than  sulphuric  acid. 

In  cases  where  much  arsenic  is  present,  it  is  advisable  to  add 
nitric  acid  in  the  proportion  of  about  1  part  HNO3  to  2  parts 
H2SO4;  this  has  the  effect  of  oxidizing  the  arsenic  to  arsenic  or 
arsenious  acid,  and  at  the  same  time  converts  hydrocyanic  into 
cyanic  acid,  thus  avoiding  the  evolution  of  large  quantities  of 
poisonous  fumes.  It  must  be  mentioned,  however,  that  under 
certain  circumstances  nitric  acid  may  lead  to  a  loss  of  gold. 
Experiments  have  shown  that  this  loss  is  greater  with  nitric  than 
with  hydrochloric  acid,  and  greater  with  hydrochloric  than  with 
sulphuric  acid.  Nitric  acid  has  sometimes  been  added  for  the 
purpose  of  dissolving  the  lead  introduced  by  the  use  of  the  lead 
zinc  couple  in  precipitating,  but  it  seems  preferable  to  remove 
this  metal  by  suitable  fluxes  in  the  subsequent  fusion. 

At  the  Metallic  Extraction  Co.'s  mill  near  Florence,  Colorado, 
a  treatment  with  hydrochloric  acid  was  given  after  roasting, 
the  roasted  precipitate  being  treated  in  a  lead-lined  sheet-steel 
pan  with  a  mixture  of  one  part  hydrochloric  acid  to  two  of  water, 
the  residue  being  afterward  filtered,  washed,  and  dried. 

After  acid  treatment,  the  precipitate  is  frequently  pumped 
to  a  filter-press,  through  which  hot  water  is  forced  to  extract  as 
much  as  possible  of  the  zinc  sulphate  still  retained,  and  finally 
dried  by  forcing  air  through  the  cakes.  The  product  may  also 
be  extracted  and  dried  by  vacuum  pans. 

The  following  is  a  description  of  the  method  employed  at  the 
Myalls  United  Mines,  Australia,  given  by  C.  J.  Morris.2  The 
zinc  is  scrubbed,  and  the  precipitate  is  placed,  together  with  the 

1  J.  E.  Thomas  and  G.  Williams,  "  Journ.  Chem.,  Met.  and  Min.  Soc.  of  South 
Africa,"  V,  334. 

2 "  Trans.  I.  M.  M.,"  XV,  543  (1906). 


ACID   TREATMENT  AND   ROASTING   OF   PRECIPITATE     263 

shorts,  in  a  wooden  acid  tank  5  ft.  deep  by  4  ft.  diameter,  pro- 
vided with  a  4-armed  revolving  paddle,  plugged  holes  for  draining 
off  the  wash,  and  a  locked  cover.  Twenty  pounds  of  acid  are 
added  to  the  charge  at  one  time,  and  a  further  quantity  when  the 
violent  action  has  ceased,  until  the  required  amount  has  been 
added.  The  charge  remains  under  treatment  all  night,  with 
occasional  stirring,  and  exhaust  steam  from  the  solution  pump 
is  led  in  through  the  cover  by  means  of  an  iron  pipe.  In  the 
morning  all  action  has  ceased,  and  twelve  times  the  bulk  of  water 
is  added,  with  agitation.  After  settling,  the  wash-water  is  drawn 
off.  This  contains  only  1  to  2  dwt.  of  gold  per  ton,  which  might  be 
recovered  by  long  settling.  The  washed  precipitate  is  then  dried 
with  addition  of  5  per  cent,  of  niter,  roasted  and  fluxed.  It  is 
claimed  that  acid  treatment,  as  described,  gives  far  better  results 
than  addition  of  niter,  roasting,  and  fusion  without  acid  treatment. 

In  many  cases  it  is  found  advisable  to  keep  the  shorts  and  fine 
precipitate  separate,  as  they  may  be  advantageously  treated  by 
different  fluxes.  At  Redjang  Lebong,  a  considerable  difference 
was  noticed  in  the  composition  of  the  bullion  obtained  from  these 
two  products.  As  the  shorts  contain  very  much  more  metallic 
zinc  than  the  fines,  they  will  naturally  require  a  larger  amount 
of  sulphuric  acid.  In  some  cases  it  is  found  that  the  solution  of 
the  zinc  by  sulphuric  acid  is  imperfect.  This  may  be  due  to  the 
metal  being  present  as  an  alloy  insoluble  in  that  acid,  or  to  the 
presence  of  protective  coatings  of  insoluble  sulphates  (PbSO4  or 
CaSOJ. 

Composition  of  Acid-treated  Precipitate.  —  The  zinc-gold  pre- 
cipitate as  generally  obtained  is  a  very  complex  mixture,  some- 
times containing,  in  addition  to  gold,  silver  and  zinc,  nearly  all 
the  common  metals,  with  silica,  carbonates,  sulphates,  sulphides, 
and  various  cyanogen  compounds ;  of  these  ingredients  the  pro- 
portions vary  enormously  in  different  samples,  so  that  no  fixed 
rules  can  be  given  as  to  the  best  method  for  its  reduction.  An 
analysis  of  acid  treated  and  roasted  precipitate  by  A.  Whitby1 
gave  the  following  percentages: 

Gold 34.5  Ferric  oxide 3.65 

Silver     4.75  Zinc  oxide    7.0 

Lead 12.5  Sulphuric  acid     6.95      (SO3) 

Copper     2.55  Nickel  oxide 1.0 

Silica    21.0 

i  "  Proc.  Chem.,  and  Met.  and  Min.  Soc.  of  South  Africa,"  III,  46  (1902). 


264  THE  CYANIDE  HANDBOOK 

(B)  ROASTING  OF  ZINC-GOLD  PRECIPITATE 

The  precipitate,  whether  acid-treated  or  not,  is  best  treated 
by  filter-pressing  or  vacuum  filtration  to  remove  as  much  of  the 
moisture  as  possible.  By  the  use  of  hot  air,  the  drying  may  be 
practically  completed  in  the  filter-press,  but  more  usually  the 
cakes  of  precipitate  are  broken  up  and  placed  on  sheet-iron  trays 
about  H  m-  deep,  on  which  the  material  is  first  carefully  dried 
over  a  slow  fire  and  finally  roasted,  either  over  an  open  grate  or 
in  a  muffle  or  reverberatory  furnace.  It  is  a  common  practice 
to  mix  about  5  per  cent,  of  niter  with  the  dried  and  powdered 
precipitate  before  roasting,  especially  in  cases  where  acid  treat- 
ment is  not  used.  The  mixture,  when  perfectly  dry,  may  be 
ignited  and  burns  of  itself,  all  carbonaceous  matter  being  thus 
removed  and  a  complete  oxidation  of  the  zinc  obtained.  Caldecott 
recommends  mixing  30  parts  of  silica  and  30  parts  of  niter  with 
every  100  parts  of  dried  precipitate;  this  yields  a  product  which 
does  not  undergo  losses  by  dusting,  and  the  sand  serves  as  a 
flux  for  the  zinc  oxide  in  the  smelting.  Other  operators  saturate 
the  precipitate,  before  drying,  with  a  strong  solution  of  niter. 

The  roasting  should  be  done  slowly,  at  a  dull  red  heat,  with 
careful  regulation  of  the  draft,  since  heavy  losses  of  gold  may 
occur  when  copious  fumes  of  zinc  are  given  off.  The  exact  amount 
of  this  loss  has  never  been  ascertained,  but  it  is  the  general  ex- 
perience that  the  best  recovery  of  the  contained  values  is  obtained 
when  the  zinc  is  eliminated  as  completely  as  possible  before 
roasting.  Stirring  may  be  occasionally  necessary  during  the 
roasting,  but  should  be  avoided  as  much  as  possible,  as  it  may 
lead  to  mechanical  losses. 

In  some  works  the  precipitate  is  placed  in  shallow  iron  pans, 
which  fit  inside  the  muffle,  and  allowed  to  remain  over  night  at  a 
moderate  heat,  with  little  or  no  stirring.  When  cool,  the  trays 
are  withdrawn  and  the  lumps  ground  and  mixed  with  the  necessary 
fluxes  for  smelting.  When  the  acid  treatment  is  very  carefully 
and  thoroughly  performed,  the  roasting  operation  is  of  less  im- 
portance, and  may  in  some  cases  be  advantageously  omitted. 
As  a  precaution  against  "  dusting  "  during  the  early  stages  of  the 
roasting,  the  precipitate  is  generally  charged  into  the  furnace  in  a 
slightly  moist  condition,  and  is  often  compressed  or  briquetted. 

Probably  more  loss  of  gold  and  silver  occurs  in  the  roasting 


ACID  TREATMENT  AND   ROASTING   OF   PRECIPITATE    265 

than  in  any  other  stage  of  the  process.  When  metallic  zinc  is 
volatilized,  it  carries  with  it  considerable  quantities  of  the  pre- 
cious metals,  probably  mechanically.  In  contact  with  the  air,  the 
zinc  vapor  burns  with  a  greenish  flame,  producing  dense  fumes 
of  white  oxide  of  zinc.  These  are  deposited  in  the  flues  and  cooler 
parts  of  the  furnace,  but  large  quantities  escape  into  the  air, 
carrying  with  them  gold  and  silver  in  a  state  of  minute  subdivision. 
Zinc  oxide  itself  is  non-volatile,  and  if  the  zinc  can  be  oxidized  by 
chemical  means  before  roasting,  this  loss  does  not  occur.  This 
is  the  chief  object  of  adding  niter  in  the  manner  described  above. 


SECTION   IV 

FLUXING,   SMELTING,    AND   REFINING   OF   THE 
PRECIPITATE 

(A)  FLUXES  FOR  ZINC-GOLD  PRECIPITATE 

THE  fluxes  to  be  used  will  depend  to  a  large  extent  on  the 
nature  of  the  materials  contained  in  the  precipitate,  and  on  the 
preliminary  treatment  which  it  has  undergone.  The  following  are 
given  as  examples,  but  in  any  case  the  most  suitable  flux  should 
be  ascertained  by  trial.  They  are  tabulated  according  to  the 
preliminary  treatment  of  the  precipitate. 

1.  For  direct  fusion  without  acid  treatment  or  roasting: 

Parts  by  weight 
(a)  (b) 

Precipitate    100  100 

Borax 35  60 

Bicarbonate  of  soda      50  7 

Sand 15  11.5 

Niter    2  to  4  19 

(a)  Julian  and  Smart,  "Cyaniding  Gold  and  Silver  Ores,"  2d  ed.,  p.  168. 

(ft)  T.  L.  Carter,  "Trans.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II, 
444. 

The  method  generally  yields  a  very-  base  bullion  containing 
much  zinc,  and  of  irregular  composition;  (6)  was  tried  for  treat- 
ment of  precipitate  from  zinc-lead  couple. 

2.  Roasting  with  niter,  without  acid  treatment: 

Parts  by  weight 
(a) 

Precipitate     100 

Borax  40 

Bicarbonate  of  soda       40 

Sand 15 

(a)  Julian  and  Smart,  loc.  cit.,  p.  168. 

When  Caldecott's  system  of  roasting  with  sand  and  niter  is 
used,  the  silica  is  omitted  from  the  flux  and  the  following  is  used: 

266 


REFINING   OF  THE   PRECIPITATE  267 

Parts  by  weight 
<*) 

Precipitate    100 

Borax 40 

Carbonate  of  soda   10 

(6)  "Journ.  Soc.  Chem.  Ind.,"  XVII,  3  (1897). 

3.  Acid  treatment  without  roasting: 

Parts  by  weight 
(a)  (&)  (c) 

.  Precipitate  .100  100  100 

Borax 25-30  66  10 

Carbonate  of  soda  50  9  40 

Fluor-spar  9  2 

Sand 15 

(a)  T.  H.  Leggett,  "Trans.  I.  M.  M.,"  V,  147. 

(6)  E.  H.  Johnson,  "Eng.  and  Min.  Journ.,"  p.  220  (1899). 

(c)  J.  Gross,  "Trans,  A.  I.  M.  E.,"  XXXV,  616. 

4.  After  acid  treatment  and  roasting:  Clay  liners  used  when  much  lead  is 
present : 

Parts  by  weight 
(a)  (6)  (c)  (d) 

Precipitate    100  100  100  100 

Fused  borax 20-35  60  70  50 

Carbonate  of  soda    25  50 

Manganese  dioxide      20-40  15-20 

Fluor-spar     5  10  0-10  10 

Sand      15-40  5  10  44 

(a)  E.  H.  Johnson  and  W.  A.  Caldecott,  "  Trans.  Chem.,  Met.  and  Min. 
Soc.  of  South  Africa,"  III,  51  (1902). 

(6)  B.  W.  Begeer,  "Metallurgy  of  Gold  on  the  Rand,"  1898. 

(c)  Used  at  Abosso  G.  M.  Co.,  Gold  Coast,  West  Africa,  1907-08,  yielding 
bullion  about  940  fine.     Previously  roasted  with  5  per  cent,  niter. 

(d)  The  present  writer  has  found  this  flux  satisfactory  for  a  base  precipi- 
tate containing  much  copper  and  lead,  together  with  sulphur  and  a  little 
arsenic. 

(B)  MIXING  OF  PRECIPITATE  AND  FLUXES 

The  various  materials  used  for  the  flux  should  be  thoroughly 
dried,  especially  the  borax  and  soda,  which  are  liable  to  contain 
considerable  amounts  of  water.  In  small  plants,  the  necessary 
quantities  for  each  charge  are  weighed  out,  mixed  on  an  iron  tray 
or  other  suitable  receptacle  with  a  scoop,  and  fed  into  the  previ- 
ously heated  crucible.  Where  large  quantities  are  dealt  with 
at  a  time  the  mixture  is  put  through  a  small  ball  mill  specially 
reserved  for  this  purpose,  so  that  the  different  ingredients  are 
thoroughly  incorporated  and  all  lumps  broken  up.  The  flux 
must  be  well  mixed  with  the  precipitate  before  transferring  to 


268  THE  CYANIDE  HANDBOOK 

the  crucible.  The  mixture  is  generally  fed  in  by  means  of  a  long 
iron  scoop,  the  lower  end  of  which  is  formed  into  a  tube  to  avoid 
loss  by  scattering  of  the  charge  while  feeding  into  the  pot. 
A  wide-necked  iron  hopper  or  funnel  is  also  used  for  this 
purpose. 

(C)  THE  FUSION  PROCESS 

The  fusion  is  almost  invariably  made  in  graphite  crucibles 
(actually  made  from  a  mixture  of  graphite  and  fire-clay),  the 
kind  known  as  "salamander"  being  frequently  used.  The  size 
of  crucible  will  depend  on  the  amount  of  fluxed  precipitate  which 
can  be  conveniently  smelted  at  one  time  in  the  furnace.  Size 
No.  60  is  largely  used.  From  10  to  20  Ib.  of  dried  precipitate 
can  be  smelted  in  one  crucible  charge.  In  cases  where  lead  is 
present,  or  when  for  any  reason  the  graphite  of  the  crucible  might 
act  injuriously  in  the  fusion,  a  "liner"  is  used,  consisting  of  a 
fire-clay  crucible  that  fits  inside  a  large  graphite  pot.  Both 
pots  and  liners  should  be  carefully  dried  and  annealed  by  gradual 
heating  outside  the  furnace,  and  raised  to  a  dull  redness  in  the 
furnace  before  charging  in  the  mixture  to  be  smelted. 

The  furnaces  used  are  square,  and  generally  similar  to  the 
wind  fusion-furnaces  used  in  assaying,  but  somewhat  larger  and 
built  so  that  the  mouth  of  the  furnace  is  flush  with  the  floor.  It 
is  a  good  plan  to  have  the  building  so  arranged  that  fuel  can  be 
supplied  to  the  furnace  and  the  ashes  removed  by  openings  out- 
side the  smelting  room  proper.  The  floor  of  the  latter  may  thus 
be  kept  clean  throughout  the  operation,  and  no  unskilled  work- 
men need  be  admitted  while  the  smelting  is  going  on,  thus  di- 
minishing the  chances  of  loss  or  theft.  The  ash-pit  should, 
however,  be  accessible  from  the  smelting  room  in  case  an  acci- 
dent should  occur,  such  as  the  breaking  or  upsetting  of  a  pot  in 
the  fire. 

The  fuel  generally  used  is  coke;  where  coal  or  charcoal  is 
employed,  the  furnace  must  be  somewhat  larger  to  allow  of  a 
sufficient  quantity  of  fuel  being  packed  round  the  crucibles. 
Furnaces  have  also  been  built  for  gasoline  or  other  liquid  fuel. 
Where  large  quantities  of  precipitate  have  to  be  smelted,  a  re- 
verberatory  furnace,  as  introduced  by  Charles  Butters,  is  some- 
times used.  Another  appliance  very  convenient  for  this  purpose 
is  a  tilting  furnace,  similar  in  design  to  that  proposed  by  H.  L. 


REFINING   OF  THE  PRECIPITATE  269 

Sulman,1  consisting  of  a  rectangular  furnace  cased  with  iron  and 
lined  internally  with  brick.  It  is  mounted  on  trunnions  and 
contains  an  inner  (replaceable)  retort  of  graphite  or  fire-clay, 
which  serves  the  place  of  the  crucible  and  holds  the  charge  to  be 
smelted.  Arrangements  are  provided,  so  that  when  the  fusion  is 
complete  the  entire  furnace  may  be  tilted  and  the  contents  of  the 
crucible  poured  into  a  mold.  A  furnace  of  this  type  was  used 
by  the  Redjang  Lebong  Mining  Co.,  for  running  down  acid-treated 
and  roasted-zinc  precipitate  containing  a  large  percentage  of  silver 
and  some  selenium.  The  latter  was  partially  expelled  as  oxide 
by  introducing  into  the  furnace  a  blast  of  air  from  an  air-com- 
pressor. There  is  considerable  saving  of  labor  and  probably  less 
risk  of  loss  in  using  some  such  arrangement,  but  the  cost  of  in- 
stallation and  repairs  is  greater  than  with  the  ordinary  pot  furnace. 

The  crucible,  in  the  usual  square  furnace,  should  be  supported 
firmly  by  a  fire-brick  resting  on  the  furnace  bars.  It  should  be 
well  packed  all  around  with  coke,  and  covered  with  a  graphite  or 
fire-clay  lid.  At  the  beginning  it  should  not  be  more  than  three- 
quarters  filled  with  the  mixture  of  flux  and  precipitate,  for  the 
charge  swells  considerably  through  the  disengagement  of  carbonic 
acid,  etc.,  as  it  becomes  heated.  After  it  is  thoroughly  melted 
it  subsides,  and  a  further  quantity  of  the  mixture  may  now  be 
added.  Toward  the  end  of  the  operation,  when  the  fusion  is 
nearly  complete,  the  contents  of  the  pot  are  stirred  with  an  iron 
rod  and  any  infusible  dross  which  remains  on  the  surface  removed 
by  skimming.  When  the  zinc  has  not  been  perfectly  removed  by 
acid  treatment,  dense  fumes  will  be  given  off  during  the  fusion,  and 
some  of  the  zinc  will  be  volatilized  and  burn  at  the  mouth  of  the 
crucible  with  a  greenish  flame.  Under  these  circumstances  some 
loss  of  gold  and  silver  by  volatilization  undoubtedly  takes  place, 
but  opinions  differ  as  to  the  extent  of  this  loss.  Deposits  of  zinc 
dust  and  zinc  oxide  carrying  high  values  are  sometimes  recovered 
from  the  flues,  and  dust  chambers  are  occasionally  used  for  col- 
lecting this  material. 

When  the  fusion  is  complete,  the  pot  is  lifted  from  the  furnace 
by  means  of  basket  tongs;  when  large  pots  are  used,  a  block  and 
tackle  arrangement  should  be  provided  for  lifting  the  pots.  The 
contents  are  then  poured  into  a  conical  mold  which  should  be 
previously  oiled  and  heated.  As  soon  as  the  bullion  has  set,  the 

i  "  Journ.  Soc.  Chem.  Ind.,"  December,  1897. 


270  THE  CYANIDE   HANDBOOK 

mold  is  inverted  onto  an  iron  tray  and  the  slag  detached  from 
the  button  of  metal  by  one  or  two  blows  of  a  hammer.  The  slag 
should  be  clear  and  uniform;  it  is  generally  of  a  light  greenish- 
gray  color,  and  is  set  aside  to  be  crushed  and  panned,  as  it  usually 
contains  sufficient  value  in  the  form  of  small  shots  of  metal  to  be 
worth  treating. 

When  the  whole  quantity  of  fluxed  precipitate  which  is  to  be 
smelted  has  been  run  down  in  this  way,  the  buttons  from  the 
conical  molds  are  remelted  in  a  clean  crucible  with  a  little  borax 
and  cast  into  an  oblong  ingot-mold.1  It  is  usual  to  take  a  sample 
of  this  bullion  just  before  casting,  by  means  of  a  dipper  formed 
from  a  piece  of  an  old  graphite  crucible.  The  molten  metal  should 
be  well  stirred  and  the  dipper  heated  before  sampling.  (See 
Part  VII.) 

(D)  USE  OF  SPECIAL  FLUXES 

Niter  is  used  to  oxidize  any  metallic  zinc  which  may  still  be 
present  in  the  precipitate  after  the  preliminary  treatment.  It  is 
generally  unnecessary  when  acid  treatment  has  been  given,  as  in 
that  case  any  zinc  remaining  is  probably  present  as  sulphate.  It 
is  ineffective  for  oxidizing  lead,  as  it  decomposes  and  gives  off 
its  oxygen  below  the  temperature  required  for  the  formation  of 
litharge. 

Manganese  dioxide  is  used  as  a  substitute  for  niter  when  lead 
is  present;  it  is  not  advisable  to  use  it  when  much  silver  is  present, 
as  it  has  a  tendency  to  carry  the  silver  into  the  slag. 

Fluor-spar  is  used  chiefly  to  give  fluidity  to  the  charge.  It 
is  also  of  some  use  in  fluxing  calcium  sulphate. 

Sand  is  added  for  the  purpose  of  forming  a  fusible  silicate  with 
the  zinc  and  other  bases  present.  It  is  omitted  when  practically 
all  the  zinc  has  been  removed  by  preliminary  operations. 

Carbonate  of  soda  is  used  only  in  small  quantity  and  is  some- 
times omitted.  When  silica  is  present  in  the  precipitate  or  has 
been  added  to  the  charge,  it  helps  by  forming  a  fusible  double 
silicate  of  zinc  and  sodium. 

Borax   is   the   principal   flux  for  all  bases  present.     It  also 

1  The  following  flux  answers  very  well  for  remelting  the  buttons  into  bars. 

Weight  of  metal  remelted    9  to  10  kilos. 

Fused  Borax   1.7  " 

Fluor-spar    0.2  " 

Niter  (added  at  moment  of  fusion)  0.15  to  0,2  " 


REFINING   OF  THE   PRECIPITATE  271 

increases  the  fluidity  of  the   charge,   apart  from   any   chemical 
action. 

(E)  TREATMENT  OF  MATTE 

It  has  already  been  noted  that  sulphur,  from  various  sources, 
is  liable  to  be  present  in  the  deposit  collected  from  the  zinc-boxes. 
Unless  the  precipitate  after  acid  treatment  is  thoroughly  roasted, 
this  sulphur,  in  the  subsequent  fusion,  will  form  a  "matte,"  gen- 
erally carrying  gold,  silver,  iron,  zinc,  and  lead,  also  copper  if 
the  latter  metal  is  present  in  the  material  treated.  This  matte 
forms  a  brittle  but  strongly  adherent  layer  above  the  button  of 
metal,  between  it  and  the  slag,  and  as  it  frequently  carries  high 
values,  some  means  must  be  found  to  reduce  it  to  a  marketable 
bullion.  Selenium,  tellurium,  arsenic,  and  antimony  form  similar 
products  when  they  occur  in  the  material  smelted. 

A  method  of  recovering  fine  bullion  from  matte  is  described 
by  A.  E.  Drucker  1  as  follows.  The  fluxes  used  for  the  reduction 
are  borax  and  cyanide.  The  matte,  borax,  and  cyanide  are  put 
separately  through  a  rock-breaker  and  crushed  fine.  Alternate 
layers  of  borax,  matte,  and  cyanide  are  charged  into  a  No.  60 
graphite  crucible  until  the  pot  is  nearly  full,  when  a  layer  of  borax 
is  added  as  a  cover.  The  crucible  is  now  put  into  the  furnace  and 
maintained  at  a  white  heat  for  two  or  three  hours,  until  the  charge 
subsides  and  bubbling  ceases.  Large  volumes  of  sulphur  are  given 
off  at  the  end  of  the  first  hour,  and  burn  at  the  mouth  of  the 
pot.  When  the  action  is  complete  the  slag  becomes  quite  thick 
and  must  be  removed  by  a  skimmer.  The  remaining  contents 
are  then  poured  into  a  conical  mold.  If  excess  of  cyanide  has 
been  used  it  forms  a  crust  just  above  the  gold  button  and  can  be 
broken  off  with  a  blow  from  a  hammer.  The  matte  is  com- 
pletely decomposed,  and  85  to  94  per  cent,  of  the  total  values 
contained  in  it  are  recovered  as  fine  metal.  Only  a  light  porous 
slag  remains,  which  may  be  remelted  with  a  subsequent  charge. 

The  usual  method  of  treating  this  matte  is  to  remelt  with 
additional  flux  and  scrap-iron,  niter  being  sometimes  added  to 
assist  in  oxidizing  the  sulphur.  This  method,  as  stated  by 
Drucker,  is  slow  and  incomplete,  and  when  graphite  crucibles  are 
used  they  are  rapidly  corroded  by  the  niter. 

i  "  Min.  Sc.  Press,"  May  18,  1907. 


272  THE  CYANIDE  HANDBOOK 

(F)  SMELTING  OF  ZINC-GOLD  PRECIPITATE  WITH  LITHARGE 

In  the  early  days  of  the  cyanide  process,  the  suggestion  of 
melting  the  zinc-precipitate  with  lead,  and  afterward  cupeling, 
seems  to  have  been  carried  out.  G.  H.  Clevenger  1  states  that  at 
the  Balbach  Smelting  and  Refining  Co.'s  plant,  Newark,  New 
Jersey,  the  precipitates,  tied  up  in  paper  sacks  in  parcels  of  1  to 
5  lb.,  were  charged  from  time  to  time  on  a  bath  of  molten  lead 
in  a  cupeling  furnace.  The  gold  and  silver  were  quickly  ab- 
sorbed by  the  lead,  and  until  the  mass  was  well  melted,  the  pre- 
caution was  taken  of  keeping  all  drafts  closed.  The  slag  was 
then  removed  by  skimming  and  the  bullion  cupeled  and  refined. 

For  this  method  it  would  seem  that  there  is  considerable  proba- 
bility of  metallic  zinc  being  volatilized  with  consequent  loss  of 
gold  and  silver.  This  is  avoided  in  P.  S.  Tavener's  process,  first 
introduced  at  the  Bonanza  mine,  Johannesburg,  in  August,  1899, 
in  which  the  precipitate,  after  filter-pressing  (but  without  acid- 
treatment  or  roasting),  is  mixed  with  litharge,  slag  from  previous 
operations,  slag  from  assay  fusions,  sand  and  sawdust,  and 
smelted  in  a  reverberatory  furnace.  The  zinc  is.  fluxed  off  with- 
out being  volatilized  to  any  appreciable  extent,  and  lead  bullion 
is  obtained  which  is  afterward  refined  on  a  bone-ash  "test,"  in 
an  ordinary  cupellation  furnace.  The  process  may  be  likened 
to  a  scorification  assay  on  a  large  scale. 

The  following  account  of  the  process  is  summarized  from  a 
detailed  description  given  by  Tavener.2  The  fine  precipitate  from 
the  filter-press  and  the  zinc  shorts  are  dried  separately  on  trays 
in  an  oven  for  15  minutes.  The  dry  precipitate  is  then  rubbed 
through  a  sieve 'of  four  holes  to  the  linear  inch,  roughly  weighed, 
and  mixed  with  the  fluxes.  These  are  as  follows : 

Parts  by  weight. 

Precipitate    100 

Litharge      60 

Assay  slag     10  to  15 

Slag  previously  used 10  to  15 

Sand 10  to  20 

After  adding  the  precipitate,  the  mixture  is  again  sifted  to  ensure 

i  "  Trans.  A.  I.  M.  E.,"  XXXIV,  891  (October,  1903). 

2"Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa"  Vol.  III.,  p.  112  (Oc- 
tober, 1902). 


REFINING   OF  THE   PRECIPITATE  273 

thorough  mixing,  and  shoveled  into  the  furnace,  which  is  as  yet 
unlighted.  The  fine  zinc  is  then  mixed  as  follows: 

Parts  by  weight. 

Fine  zinc  (shorts)      100 

Litharge      150 

Slag    20 

This  is  put  into  the  furnace  on  the  top  of  the  precipitate  to  pre- 
vent 'loss  by  dusting  and  also  to  ensure  the  greater  part  of  the 
litharge  being  on  the  top  of  the  charge.  A  slow  fire  is  now  lighted 
and  the  charge  allowed  to  dry  for  a  couple  of  hours.  The  temper- 
ature is  then  raised,  and  in  four  or  five  hours  the  charge  is  reduced; 
any  sweepings  or  by-products  which  have  to  be  worked  up  are 
now  added,  and  are  quickly  absorbed.  When  the  slag  has  again 
become  fluid,  it  is  well  stirred  with  a  rabble,  and  sawdust  thrown 
in  to  reduce  the  excess  of  litharge.  The  slag  is  now  tapped  off 
through  the  slag-door  above  the  level  of  the  lead,  and  the  latter 
is  skimmed;  a  shovelful  of  lime  is  thrown  in  and  a  final  skimming 
is  given.  The  clean  lead-bath  is  then  stirred  and  sampled,  the 
tap-hole  is  opened,  and  the  lead  bullion  run  into  molds. 

The  lead  bullion  is  now  cupeled  on  a  test,  consisting  of  an 
oval  cast-iron  frame  filled  with  bone-ash  ground  to  pass  a  20-mesh 
screen,  and  mixed  with  3  per  cent,  caustic  potash  and  10  to  11 
per  cent,  water.  The  mixture  is  again  sifted  to  break  up  lumps. 
The  test-frame  is  placed  on  a  cast-iron  plate  and  filled  with  the 
bone-ash,  which  is  then  tamped  in.  The  center  is  then  hollowed 
out,  leaving  a  rim  round  the  sides.  About  300  Ib.  of  bone-ash  are 
used  for  one  test,  which  may  be  used  about  four  times,  cupeling 
altogether  over  1\  tons  of  lead  bullion.  The  test  should  be  dried 
slowly  for  some  weeks  before  use. 

When  a  new  test  is  put  in  the  furnace,  a  slow  fire  is  kept  up 
for  3  or  4  hours.  An  iron  blast-pipe,  3  in.  diameter,  flattened  and 
turned  down  at  one  end  to  allow  the  blast  to  strike  on  the  molten 
lead,  is  now  fitted  to  the  back  end  of  the  cupel.  Temperature  is 
raised,  and  the  lead  bars  fed  in  one  at  a  time  through  the  working- 
door  of  the  furnace  onto  the  test.  A  channel  is  cut  in  the  rim  of 
the  latter  }  to  \  in.  deep  and  1 J  in.  wide,  and  communicating  with 
a  hole  by  which  the  molten  litharge  runs  down  to  a  suitable  pot 
placed  beneath.  When  the  test  is  filled  with  molten  lead  nearly 
to  the  level  of  this  channel,  the  temperature  is  increased  to  the 
melting-point  of  litharge,  and  when  the  lead  is  covered  with  molten 


274  THE  CYANIDE  HANDBOOK 

litharge  the  blast  is  turned  on,  and  the  litharge  allowed  to  flow 
away  along  the  channel,  which  is  deepened  as  the  operation 
proceeds.  Fresh  lead  bars  are  fed  in  until  all  are  melted.  The 
temperature  is  raised  as  the  proportion  of  gold  in  the  alloy  re- 
maining on  the  cupel  increases.  At  the  finish  it  is  necessary  to 
add  a  little  assay-slag,  which  is  melted  and  run  off.  When  the 
operation  is  complete,  the  gold  freezes  or  solidifies.  It  is  then 
broken  in  pieces,  remelted  in  crucibles,  and  cast  into  bars. 

This  method  possesses  many  advantages  over  the  ordinary 
systems  of  reducing  zinc-gold  precipitate.  The  cost  of  material 
is  much  lower;  a  large  part  of  the  litharge  is  recovered  for  re-use, 
and  the  slag  used  as  flux  in  this  process  is  a  waste  product  from 
which  the  contained  values  could  otherwise  be  obtained  only  at  a 
high  cost.  It  also  affords  a  means  of  easily  disposing  of  a  num- 
ber of  troublesome  by-products  of  the  mill  and  cyanide  works 
which  cannot  be  economically  treated  by  other  methods.  The 
cost  of  installation,  however,  is  so  high  that  the  method  could 
only  be  economically  carried  out  on  a  large  scale;  moreover, 
skilled  labor  is  required,  especially  in  the  cupellation  process.  The 
method  would  seem  in  general  to  be  more  suitable  for  customs 
works  than  for  individual  mines.  In  spite  of  the  fact  that  com- 
parative tests  made  with  great  care  showed  a  much  higher  recovery 
by  the  litharge-smelting  process  as  compared  with  the  ordinary 
acid-treatment,  roasting,  and  smelting  the  system  has  not  been 
generally  adopted.  In  some  plants,  where  the  ordinary  method  of 
smelting  is  used,  it  is  customary  to  remelt  all  the  slags  from  the 
first  fusion  of  precipitate,  with  litharge  and  a  little  additional  flux, 
adding  a  reducing  agent  if  necessary  or  adding  a  small  quantity 
of  metallic  lead  at  the  finish.  The  resulting  lead  bullion  is  then 
cupeled. 

(G)  NATURE  AND  PROPERTIES  OF  CYANIDE  BULLION 

The  bullion  bars,  after  the  final  smelting,  are  frequently  turned 
out  of  the  ingot  molds  into  a  vessel  of  water  as  soon  as  they  are 
set.  The  adhering  slag  is  detached  by  hammering,  and  in  some 
cases  the  bar  is  "  pickled  "  by  immersing  in  dilute  nitric  acid  and 
cleaned  by  scrubbing  with  a  hard  brush.  If  dip  samples  have 
not  been  taken,  it  is  commonly  sampled  by  machine  drill  as 
described  below,  in  Part  VII,  and  then  immediately  packed  for 
shipment. 


REFINING   OF  THE   PRECIPITATE  275 

The  nature  and  composition  of  the  bullion  varies  according 
t.>  the  proportion  of  gold  and  silver,  and  to  the  method  by  which 
it  has  been  obtained.  When  much  zinc  is  present,  it  is  of  a  pale 
yellowish-green  color,  and  shows  much  variation  in  composition 
of  different  parts  of  the  bar,  the  general  tendency  being  for  the 
gold  value  to  concentrate  toward  the  center  of  the  bar.1  This 
refers  chiefly  to  bars  of  650  to  800  fineness;  with  richer  bars  the 
liquation  is  less  marked.  It  is  quite  possible  to  obtain  cyanide 
gold  which  is  little,  if  at  all,  inferior  to  battery  gold  in  fineness. 
This  is  mainly  a  question  of  care  in  the  clean-up  and  smelting, 
more  particularly  in  the  thorough  extraction  of  metallic  zinc  by 
acid  treatment  and  in  the  selection  of  the  proper  fluxes  in  the 
fusion  process. 

The  following  analyses,  given  by  Dr.  T.  Kirke  Rose,2  will 
illustrate  the  character  of  bullion  produced  when  direct  smelting 
is  used  without  preliminary  treatment  to  remove  the  zinc: 

(1)  (2)  (3) 

Per  cent.  Per  cent.  Per  cent. 

Gold     60.3  61.7  72.6 

Silver     7.3  8.1  9.2 

Zinc    15.0  9.5  7.1 

Lead 7.0  16.4  4.9 

Copper     6.5  4.0  4.8 

Iron 2.2  0.3  1.4 

Nickel    2.0 

By  acid  treatment  and  roasting  the  amount  of  impurity  may 
be  reduced  to  5  or  6  per  cent.,  particularly  if  manganese  dioxide 
be  used  for  fluxing  off  the  lead. 

(H)  REFINING  OF  BULLION 

On  account  of  the  deductions  made  by  bullion  buyers,  con- 
siderable efforts  have  been  made  to  devise  a  means  of  economically 
purifying  the  low-grade  bullion  produced  by  the  cyanide  process. 
It  may  be  remarked,  however,  that  it  is  generally  easier  and 
more  satisfactory  to  remove  the  impurities  before  conversion  into 
bullion  than  after. 

The  method  of  remelting  with  borax  is  very  ancient,  as  is  also 
the  practice  of  sprinkling  borax  on  the  metal  at  the  moment  of 
fusion. 

1  See  paper  by  F0  Stockhausen,  "  Proc.  Chem.  Met.  and  Min.  Soc.  of  South 
Africa,"  II,  46. 

2  "Metallurgy  of  Gold,"  4th  edition,  p.  331. 


276  THE  CYANIDE  HANDBOOK 

Refining  by  leading  a  current  of  chlorine  gas  through  the 
molten  bullion  was  practised  for  many  years  in  dealing  with 
battery  gold  in  Australia,  where  it  was  introduced  by  Miller  in 
1867  and  used  at  the  Sydney  mint.  The  process  was  in  use  at 
the  Pretoria  mint  at  one  time  for  refining  cyanide  bullion,  but 
has  the  drawback  that  it  involves  a  separate  operation  for  the 
recovery  of  the  silver,  as  the  scoria  formed  contains  this  metal 
as  chloride. 

Dr.  T.  Kirke  Rose  l  has  experimented  on  a  method  of  refining 
by  injecting  oxygen  gas  into  the  molten  metal.  Air  may  also 
be  used,  and  is  equally  effective  in  removing  base  metals,  but  the 
action  is  slower.  The  method  is  also  applicable  to  zinc-gold 
precipitate  without  previous  smelting;  sand,  borax,  and  charcoal 
are  added,  the  mixture  fused  in  a  graphite  pot  with  clay  liner, 
and  air  or  oxygen  injected  into  the  molten  mixture  through  a 
J-in.  clay  pipe,  by  means  of  a  Root's  blower. 

i  "  Trans.  I.  M.  M.,"  XIV,  378-441  (April,  1905). 


PART  VI 
SPECIAL  MODIFICATIONS  OF  THE  CYANIDE  PROCESS 

THIS  part  of  the  book  will  be  devoted  to  the  discussion  of 
certain  departures  from  the  normal  course  of  cyanide  treatment 
adopted  in  particular  cases  and  under  special  circumstances. 
We  shall  refer  briefly  to  certain  new  developments  of  the  process 
which  have  not  yet  stood  the  test  of  experience  long  enough  to 
demonstrate  their  practical  value.  Some  account  will  likewise 
be  given  of  obsolete  or  nearly  obsolete  methods  which  possess 
a  historical  interest  for  cyanide  workers.  As  the  admission  of 
such  descriptions  may  be  criticized,  it  may  be  pointed  out  that 
all  improvements  in  the  cyanide  process  are  merely  applications 
of  well-known  principles  employed  in  other  branches  of  industry; 
that  much  may  be  learned  by  studying  the  causes  of  past  failures; 
and  that  the  experience  of  the  past  often  points  out  the  directest 
road  to  advance  in  the  future. 

These  special  processes  will  be  considered  under  the  following 
heads:  (1)  Direct  treatment  after  dry  or  wet  crushing.  (2) 
Crushing  with  cyanide  solution.  (3)  Roasting  before  cyanide 
treatment.  (4)  Use  of  auxiliary  dissolving  agents.  (5)  Elec- 
trolytic precipitation  processes.  (6)  Other  precipitation  processes 
(7)  Special  treatment  of  cupriferous  ores. 


SECTION  I 
DIRECT  TREATMENT  AFTER  DRY  OR  WET  CRUSHING 

DIRECT  treatment  may  be  defined  as  any  process  in  which  the 
ore  is  crushed  dry  or  with  water,  and  the  cyanide  solution  applied 
at  once  to  the  crushed  product,  the  latter  undergoing  no  amalga- 
mation, hydraulic  separation,  concentration,  roasting,  or  other 
intermediate  process  previous  to  cyanide  treatment.  When  this 
system  is  adopted,  dry  crushing  is  nearly  always  employed  in 
preference  to  wet,  chiefly  because  the  wet-crushed  product  is 
seldom  in  a  condition  suitable  for  cyanide  treatment  as  a  whole, 
being  generally  unleachable  without  some  form  of  hydraulic 
separation;  also  because  the 'cost  of  plate  amalgamation  is  gen- 
erally so  trifling  in  comparison  with  that  of  crushing,  that  there 
is  no  sufficient  advantage  in  omitting  it  in  the  case  of  wet-crushed 
ore. 

For  diy  crushing,  Chilian,  Griffin  or  Ball  mills  and  rolls  are 
preferable  to  stamps.  Some  particulars  with  regard  to  these 
machines  are  given  in  Part  III.  The  system  is  particularly 
suitable  for  cases  in  which  the  ore  is  exceptionally  friable  or  porous; 
in  such  cases  good,  extractions  can  sometimes  be  obtained  even  with 
very  coarse  crushing,  as  at  the  Mercur  mine,  Utah,  where  the 
oxidized  ore  was  treated  direct  after  dry  crushing  to  J-in.  size. 
At  the  George  and  May  mine,  Johannesburg,  a  porous  oxidized  ore 
was  crushed  coarsely  in  a  Gates  crusher  and  treated  direct  by 
cyanide,  giving  an  extraction  of  70  per  cent,  of  the  gold.1  At  the 
Lisbon  Berlyn  mine,  Lydenburg,  Transvaal,  a  10  dwt.  ore  was 
put  through  a  Blake  rock-breaker,  Marsden*  fine  crusher,  and 
Gates  rolls;  the  product  gave  a  68  per  cent,  extraction  by  direct 
cyanide  treatment. 

It  is  generally  necessary  to  dry  the  ore  sufficiently  to  reduce 
the  percentage  of  moisture  below  2  per  cent,  previous  to  dry 
crushing,  care  being  taken  in  this  operation  to  avoid  partial  roast- 

i  Julian  and  Smart,  loc.  tit.,  p.  202. 
279 


280  THE  CYANIDE  HANDBOOK 

ing,  which  might  lead  to  the  formation  of  cyanicides.  To  avoid 
the  formation  of  large  amounts  of  fine  dust,  the  crushing  is  best 
done  in  several  stages,  using  screens  and  returning  the  oversize  for 
recrushing.  As  a  rule,  shallow  tanks  must  be  used  for  the  leach- 
ing of  the  dry-crushed  product,  and  in  many  cases  nitration  is 
aided  by  suction.  Since  no  moisture  has  to  be  displaced  by  solu- 
tion, it  is  possible  to  give  a  more  thorough  final  water-wash  than 
is  the  case  when  wet  crushing  is  used,  without  increasing  the  stock 
of  solution  in  the  plant. 


SECTION   II 
CRUSHING    WITH   CYANIDE  SOLUTION 

GENERAL  CONSIDERATIONS 

THE  crushing  of  ore  with  cyanide  solution  instead  of  water 
was  attempted  at  least  as  early  as  1892,  when  experiments  in 
this  direction  were  made  at  the  May  Consolidated  Battery  near 
Johannesburg.1  The  system  was  introduced  at  the  Crown  mine, 
Karangahake,  New  Zealand,  in  1897,  and  at  Central  City,  South 
Dakota,  in  1899.  Five  mills  on  this  principle  were  established 
in  South  Dakota  in  1904,  since  when  the  method  has  been  ex- 
tensively adopted  in  the  United  States  and  Mexico. 

The  early  attempts  at  crushing  with  cyanide  seem  to  have 
been  abandoned  on  account  of  difficulties  in  handling  slimes. 
The  proportion  of  ore  to  liquid  in  the  material  crushed  is  neces- 
sarily much  greater  than  when  water  is  used,  and  it  is  of  course 
impossible  to  run  the  slimes  to  waste  without  losing  the  greater 
part  of  the  dissolved  values.  Owing  to  the  thicker  pulp,  the  ore 
is  also  crushed  finer  than  when  water  is  used  under  ordinary 
conditions,  and  the  product  is  therefore  less  adapted  for  direct 
leaching.  In  modern  practice,  however,  these  difficulties  are 
overcome  by  a  system  of  hydraulic  separation,  in  which  the  clear 
overflow  is  returned  to  the  mill  and  the  sand  and  slime  collected 
for  separate  treatment.  To  avoid  the  necessity  of  handling 
enormous  volumes  of  solution,  the  amount  of  liquid  used  in  the 
battery  is  generally  from  1^  to  1  ton  of  solution  per  ton  of  ore 
crushed,  but  as  much  as  7  tons  is  sometimes  used. 

The  advantages  of  the  system  are  briefly  as  follows:  (1)  The 
solution  of  gold  begins  from  the  moment  the  ore  enters  the  battery. 
(2)  There  is  no  necessity  for  special  appliances  for  agitation  and 
aeration,  these  being  sufficiently  secured  by  the  transfer  of  the 
pulp  from  the  battery  to  the  classifiers  and  treatment  tanks. 

l"  E.  and  M.  J.,"  Oct.  8,  1892. 
281 


282  THE  CYANIDE  HANDBOOK 

(3)  Less  water  is  required  than  when  the  crushing  is  done  in 
water.  (4)  There  is  no  necessity  for  running  any  solution  to 
waste,  as  must  be  generally  done  when  final  water-washes  are 
given  in  the  ordinary  system  of  treatment. 

The  objections  are:  (1)  There  is  danger  of  loss,  owing  to  the 
fact  that  gold  in  solution  is  transferred  for  a  considerable  dis- 
tance and  through  a  number  of  different  appliances.  (2)  Owing 
to  the  thickness  of  the  battery  pulp,  the  capacity  of  the  mill  is 
reduced,  and,  as  already  pointed  out,  a  larger  percentage  of  fines  is 
produced.  (3)  The  action  of  the  cyanide  hardens  the  amalgam 
on  the  plates,  and  corrodes  the  plates  themselves,  owing  to  the 
solvent  action  of  cyanide  on  copper.  (4)  It  is  impossible  to  give 
preliminary  water  or  alkali  washes.  This  is  a  serious  objection 
in  the  case  of  acid  ores,  or  of  ores  containing  soluble  cyanicides, 
which  might  be  removed  by  preliminary  treatment  in  the  ordinary 
process. 

The  first  objection  is  not  of  much  consequence  in  a  well-con- 
structed plant,  where  proper  means  are  taken  to  prevent  leakage; 
the  second  is  of  little  importance  in  the  case  of  ores  which  must 
be  crushed  fine  in  any  case  in  order  to  obtain  a  good  extraction. 
When  very  dilute  solutions  (.03  to  .07  per  cent.  KCN)  are  used, 
as  is  generally  the  case,  the  action  on  the  plates  is  not  serious, 
and  it  may  possibly  be  avoided  by  using  Muntz  metal  or  some 
other  alloy  instead  of  copper. 

Illustrations  from  Practical  Working 

On  the  Rand,  the  system  of  crushing  with  cyanide  solution 
forms  part  of  the  scheme  of  treatment  introduced  by  G.  A. 
and  H.  S.  Denny.1  In  this  system  the  ore  is  crushed  with  a 
solution  containing  .03  per  cent,  cyanide  (as  KCy)  and  .004  per 
cent,  alkali  (calculated  as  NaOH),  in  the  proportion  of  6.6  tons 
of  solution  to  1  ton  of  ore.  After  passing  over  amalgamated 
plates,  the  pulp,  mixed  with  the  returned  coarse  product  from 
the  spitz kasten  following  the  tube  mills,  goes  to  hydraulic  classi- 
fiers, where  coarse  sand  and  concentrates  are  separated  from  fine 
sand  and  slime.  The  coarse  sand  and  concentrates  are  passed 
through  tube  mills,  and  thence  over  shaking  amalgamated  plates 
to  spitzkasten,  the  overflow  from  which  goes  to  the  conical  slime 
settlers,  while  the  underflow  (coarse  product)  is  elevated  and 

i "  E.  and  M.  J.,"  LXXXII,  1217  (Dec.  29,  1906> 


CRUSHING   WITH  CYANIDE  SOLUTION  283 

returned  to  the  pulp  leaving  the  battery  plates.  The  fine  sand 
and  slimes  go  through  another  set  of  spitzkasten,  from  which  the 
sandy  product  goes  to  percolation  tanks,  while  the  slimy  portion 
goes  to  a  large  conical  tank,  whence  the  clear  solution  overflows 
and  is  returned  to  a  solution  tank  supplying  the  battery.  The 
thickened  slime-pulp,  together  with  the  slime  overflow  from  the 
tube-mill  product,  goes  to  conical  slime  settlers  and  is  then 
pumped  to  filter-presses.  The  precipitated  solutions  are  also 
returned  to  the  mill-supply  tank. 

This  system  could  only  be  successfully  applied  in  cases  where 
the  gold  in  the  finely  crushed  ore  is  very  rapidly  dissolved;  on  the 
Rand  it  is  claimed  that  98  per  cent,  of  the  gold  recovered  from 
the  slime  is  dissolved  before  the  slime  is  settled,  and  that  70  per 
cent,  of  the  gold  recovered  from  sands  is  in  solution  before  per- 
colation begins.  In  the  pulp  leaving  the  mortar-boxes  12.65 
per  cent,  of  the  total  gold  is  already  in  solution. 

The  results  of  a  month's  treatment  at  the  Meyer  and  Charlton 
G.  M.  Company's  plant,  working  on  this  system,  are  given  as 
follows: 

Ore  treated     10,740  tons 

Average  assay  before  treatment    $10.90  per  ton 

Average  assay  of  residues $  0.51     "     " 

Extracted  011  battery  plates      43.85  per  cent. 

"         on  shaking  plates    3.01     "       " 

"         in  sand  treatment     9.76    " 

"         from  ore  in  transit    38.67    "      " 

Total  extraction 95.29 

Of  the  total  ore  milled,  52.3  per  cent,  is  reground  in  tube  mills; 
approximately  70  per  cent,  is  treated  by  percolation  as  fine  sand, 
and  30  per  cent,  as  slime.  It  will  be  noticed  that  comparatively 
little  of  the  gold  is  recovered  from  the  sand  in  the  percolation 
process,  most  of  it  having  been  already  dissolved  and  carried  off 
with  the  solution  in  the  slime  overflow.  This  suggests  a  further 
modification  of  the  process,  in  which  percolation  is  eliminated 
altogether,  and  the  whole  of  the  ore  ground  fine  enough  to  be 
treated  by  settlement,  decantation  of  clear  solution,  and  filter- 
pressing  of  the  settled  pulp.  It  is  doubtful,  however,  whether  the 
reground  sand  would  in  all  cases  yield  its  gold  values  to  the  solu- 
tion as  rapidly  as  is  the  case  with  true  slime.  In  ores  where  the 
values  are  less  rapidly  dissolved,  some  form  of  mechanical  agitation 
and  aeration  will  generally  be  necessary. 


284  THE  CYANIDE  HANDBOOK 

In  the  United  States,  similar  methods  have  been  adopted  at  the 
Liberty  Bell  mine,  Colorado,  and  at  various  plants  in  the  Black 
Hills,  South  Dakota,  and  in  Nevada.  In  cases  where  the  finely 
ground  pulp  is  treated  by  suction  filters  on  the  Moore  or  Butters 
principle,  it  is  found  advisable  to  pass  the  overflow  from  the  first 
set  of  hydraulic  cone  classifiers  through  a  second  set,  returning 
the  coarse  products  from  each  set  for  regrinding,  or  delivering 
them  to  the  leaching  tanks,  and  allowing  only  the  fine  product 
from  the  second  classifiers  to  go  to  the  slime  filter  tank.  It  is 
found  that  these  filters  are  best  adapted  for  treating  slime  which 
is  as  free  as  possible  from  fine  sand.1  The  presence  of  a  little 
slime  in  the  sand  treated  by  percolation  is  of  less  consequence, 
as  the  material  is  very  thoroughly  mixed  by  the  use  of  the  Blais- 
dell  sand  distributor  and  by  double  treatment. 

In  the  Black  Hills,2  on  the  other  hand,  where  the  Merrill 
filter-press  is  in  use,  the  practice  is  to  make  as  clean  a  sand  as 
possible.  The  stream  of  pulp  is  passed  through  a  succession  of 
cones,  the  final  ones  being  arranged  as  spitzlutten  —  that  is,  they 
have  an  upward  stream  of  solution  introduced  at  the  bottom. 
The  fine  product  treated  by  filter-pressing  contains  15  to  20  per 
cent,  of  sand  passing  a  150-mesh  screen.  The  battery  pulp  is 
delivered  to  the  cones  by  means  of  sand  pumps,  and  solution  is 
added  in  the  launder  which  carries  the  sands  to  the  distributor, 
so  as  to  dilute  the  pulp  in  the  ratio  of  5  to  1.  The  battery  solu- 
tion has  a  strength  of  .06  to  .065  per  cent.  KCN  and  .04  per  cent. 
NaOH;  the  solution  after  precipitation  carries  .075  to  .08  per 
cent.  KCN  and  .05  to  .06  per  cent.  NaOH.  (These  figures  refer 
to  the  practice  at  the  Maitland  properties,  South  Dakota,  in 
1904.) 

At  the  Desert  mill  (Tonopah  Mining  Company),  Millers, 
Nevada.3  the  ore  is  crushed  with  a  .15  per  cent,  solution,  using 
7  tons  solution  per  ton  of  ore.  The  pulp  is  concentrated  on  Wilfley 
tables,  the  tailings  from  which  pass  to  cone  hydraulic  classifiers, 
and  clean  slime  is  separated  from  them  as  already  described. 
The  sand  goes  to  collecting  vats,  in  which  it  is  drained.  It  is  then 
excavated  by  the  Blaisdell  apparatus  and  carried  by  conveyors 

1  This  is  contrary  to  the  experience  in  other  localities,  where  a  small  proportion 
of  fine  sand  in  the  slime  is  found  to  be  essential  to  the  successful  working  of  suc- 
tion filters. 

2  J.  Gross,  "Trans.  A.  I.  M.  E.,"  XXXV,  616. 
s  A.  R.  Parsons,  "  Min.  Sci.  Press,"  XCV,  494. 


CRUSHING   WITH  CYANIDE  SOLUTION  285 

to  leaching  vats;  lime  is  added  in  the  collecting  vats  and  lead 
acetate  during  the  transfer.  The  solutions  used  in  leaching  con- 
tain .25  to  .15  per  cent.  KCN.  After  five  days'  treatment,  includ- 
ing transfer,  the  sand  is  passed  to  a  second  set  of  vats  and  similarly 
treated  for  another  five  days,  then  to  a  third  set  for  three  to  five 
days,  the  total  time  of  treatment  being  twelve  to  fifteen  days. 
The  residue  carries  0.6  dwt.  gold  and  3.1  oz.  silver.  The  slime 
is  collected  in  vats  of  36  ft.  diameter  by  20  ft.  deep,  with  rim 
overflow,  the  clear  solution  being  returned  to  the  battery  storage 
tank.  The  thickened  pulp  goes  to  agitation  vats  previously 
filled  with  precipitated  solution,  to  which  the  requisite  quantities 
of  lime  and  cyanide  have  been  added.  Agitation  is  continued 
for  thirty  hours,  assisted  by  injection  of  compressed  air  and  cir- 
culation with  centrifugal  pump,  the  dilution  of  pulp  being  about 
4  to  1.  After  settling  for  six  hours,  the  clear  solution  is  drawn 
off  for  precipitation  and  the  slime  is  agitated  with  fresh  solution 
for  a  further  twenty-four  hours,  after  which  it  goes  to  the  Butters 
filter  plant. 

In  Mexico,  the  process  is  in  use  at  various  plants  treating  gold 
and  silver  ores.  At  Butters'  Copala  mines,  Sinaloa,  the  ore  treated 
carries  gold  $1.96  and  silver  15.8  oz.  It  is  crushed  by  stamps 
with  12-mesh  screens,  with  a  solution  containing  .07  per  cent. 
NaCN  and  .135  per  cent,  alkali  calculated  as  NaOH,  using  16  tons 
of  solution  per  ton  of  ore.  The  battery  product  goes  to  cone 
classifiers,  from  which  the  coarse  product  goes  to  tube  mills  and 
the  fine  product  to  a  second  classifier.  The  coarse  product  from 
the  latter  also  goes  to  the  tube  mills,  the  effluent  from  which 
returns  to  the  second  classifier.  The  fine  product  from  the  second 
classifier  goes  to  a  third,  which  makes  the  final  separation  of  42 
per  cent,  sand  58  per  cent,  slime.  The  sand  is  leached  with  0.3 
per  cent.  NaCN,  and  the  slime  is  treated  in  agitation  vats  and 
Butters  filters. 


SECTION  III 

ROASTING   BEFORE   CYANIDE  TREATMENT 

THE  conditions  under  which  roasting  is  necessary  before 
cyanide  treatment  have  been  briefly  referred  to  in  Part  III  of 
this  book.  In  general,  it  may  be  stated  that  roasting  is  only 
necessary  or  advantageous  in  cases  where  the  gold  is  combined, 
or  closely  associated,  with  some  element  which  prevents  or  re- 
tards its  solution  in  cyanide.  The  chief  applications  of  roasting  in 
practice  are:  (1)  to  telluride  ores,  such  as  those  of  Cripple  Creek 
and  Western  Australia,  where  some  part  of  the  gold  is  probably 
in  chemical  combination  with  tellurium,  the  compound  being 
unattacked  by  ordinary  cyanide  solution,  even  in  presence  of 
excess  of  dissolved  oxygen;  (2)  to  arsenical  sulphide  ores,  such  as 
those  of  the  Mercur  district,  Utah. 

Two  types  of  furnace  are  in  general  use,  viz.:  (1)  furnaces 
with  single  or  superimposed  hearths  and  revolving  rabbles,  such 
as  the  Edwards  and  Merton  furnaces;  (2)  furnaces  consisting  of 
an  inclined  revolving  cylinder,  such  as  the  Argall  roaster.  Roast- 
ing by  hand  in  reverberatory  furnaces  was  formerly  employed 
as  a  preliminary  operation  in  the  cyaniding  of  concentrates  on 
the  Rand  and  elsewhere,  but  is  now  superseded  in  most  parts  of 
the  world  by  mechanical  contrivances. 

FURNACES  WITH  REVOLVING  RABBLES 

The  Edwards  furnace  consists  of  a  single  hearth  enclosed  in 
an  iron  framework,  and  supported  above  the  ground  on  central 
pivots,  which  enable  the  hearth  to  be  tilted  to  any  required  angle 
to  aid  the  passage  of  the  ore  along  the  bed  of  the  furnace.  The 
furnace  is  kept  at  the  desired  inclination  by  means  of  screw- 
jacks.  The  rabbles  are  supported  on  vertical  shafts  passing 
through  the  roof  of  the  furnace,  and  are  driven  by  means  of  a 
horizontal  shaft  and  gear-wheels  above  the  furnace.  To  these 
vertical  shafts  are  attached  a  number  of  removable  plows  or  rakes, 

286 


ROASTING   BEFORE  CYANIDE  TREATMENT  287 

so  arranged  that  each  revolves  in  the  opposite  direction  to  the 
succeeding  one.  The  ore  is  thus  made  to  travel  across  the  fur- 
nace in  a  zigzag  direction.  In  some  cases  the  five  rabbles  nearest 
the  fire-box  are  water-cooled;  the  shafts  are  made  hollow  and  a 
stream  of  water  is  allowed  to  descend  through  the  central  pipe, 
pass  through  a  cavity  in  the  rabble  itself,  and  escape  into  a  cir- 
cular channel  surrounding  the  vertical  shaft  above  the  furnace 
arch. 

The  ore  is  fed  in  at  the  receiving  end  of  the  furnace  by  means 
of  fluted  rolls,  consisting  of  cast-iron  cylinders  having  eight  V-- 
shaped channels  on  the  circumference;  these  rolls  are  driven 
by  toothed  gearing.  The  rabbles  then  gradually  work  the  ore 
toward  the  discharge  end  (nearest  the  fire-box),  where  the  heat 
is  greatest.  The  roasted  ore  is  finally  discharged  through  an 
opening  on  to  a  "  push  conveyor."  This  consists  of  a  semicircular 
trough  provided  with  transverse  blades  free  to  move  only  in  one 
direction.  The  conveyor  moves  horizontally  to  and  fro  on 
rollers,  and  at  each  forward  movement  the  ore  is  pushed  by  the 
blades  a  distance  of  20  in.;  on  the  return  movement  the  blades  are 
free  to  swing  and  pass  back  over  the  heaps  of  ore  formed  by  the 
forward  movement.  The  ore  is  thus  gradually  pushed  to  the 
end  of  the  trough,  and  at  the  same  time  turned  over  by  the  blades, 
thus  exposing  fresh  surfaces  and  allowing  an  opportunity  for 
improving  the  final  roast.  The  roasted  ore  is  then  ready  for 
cyanide  treatment,  and  may  be  discharged  directly  from  the  con- 
veyor into  a  stream  of  solution.1 

The  Merlon  furnace  has  three  superimposed  horizontal  hearths 
connected  by  vertical  discharge  holes.  The  rabbles,  as  in  the 
Edwards  furnace,  are  carried  by  vertical  shafts,  of  which  there 
are  four  or  five,  each  shaft  passing  through  the  whole  series  of 
hearths,  and  being  mounted  at  the  lower  end  on  a  footstep  below 
the  bottom  hearth.  Attached  to  each  shaft  are  three  rabbles, 
one  on  each  hearth,  arranged  so  that  the  radii  of  the  circles  they 
describe  in  revolving  are  a  little  less  than  the  distance  between 
the  shafts.  By  this  means  the  ore  is  passed  successively  from 
one  rabble  to  the  next,  and  eventually  falls  through  the  discharge 
door  on  to  the  hearth  below.  A  sliding  bar  at  the  discharge 
doors  regulates  the  rate  of  discharge.  There  is  also  a  finishing 
hearth  next  the  fire-box,  with  rabbles  which  are  sometimes  water- 

i  E.  W.  Simpson  in  "  Trans.  I.  M.  M.,"  XIII,  27-33. 


288  THE  CYANIDE  HANDBOOK 

jacketed.  The  vertical  shafts  are  driven  by  bevel  or  worm- 
gearing  at  1  to  2  r.p.m.,  and  are  provided  with  special  arrange- 
ments for  counteracting  the  effect  of  expansion. 

The  Merton  furnace  is  more  economical,  both  in  first  cost  and 
in  working,  than  the  Edwards,  but  has  the  disadvantage  that  the 
inclination  of  the  hearths  cannot  be  varied.  There  is  also  more 
difficulty  in  withdrawing  the  shafts  of  the  rabbles  for  repair. 
Doors  are  provided  at  the  ends  and  sides  for  admitting  air  and 
for  removing  and  renewing  the  rabbles.  The  capacity  of  this 
furnace  varies  from  5  to  25  tons  per  day,  for  ores  containing 
from  25  to  6  per  cent,  of  sulphur.  The  roasting  is  very  perfect, 
and  the  percentage  of  sulphur  may  be  reduced  to  .05  per  cent, 
or  less.1  In  Australia  the  fuel  used  is  generally  eucalyptus  wood, 
but  oil  or  gas  may  be  used  with  advantage,  and  give  a  more  regu- 
lar temperature.  The  accompanying  drawing  (Fig.  38)  shows 
a  recent  type  of  this  furnace  in  plan  and  sectional  elevation. 

REVOLVING  CYLINDRICAL  FURNACES 

Several  furnaces  of  this  type  have  been  in  use  for  many  years 
for  roasting  ores  for  the  chlorination  process,  as,  for  example, 
the  Bruckner  cylinder.  Most  of  these,  however,  are  costly,  both 
in  initial  expense  and  in  repairs.  We  shall  here  describe  only 
the  Argall  roaster,  which  has  been  successfully  applied  in  pre- 
paring for  cyanide  treatment  the  ores  of  the  Cripple  Creek  district, 
Colorado.  A  similar  apparatus  is  used  as  a  drier  for  ore  previous 
to  crushing  in  rolls.  The  furnace  consists  of  four  or  more  parallel 
steel  tubes  lined  with  brick  or  tile,  fire-brick  being  used  in  the  parts 
exposed  to  the  greatest  heat.  These  tubes  are  mounted  together, 
so  as  to  revolve  as  a  single  cylinder  supported  on  two  tires. 
The  latter  revolves  on  friction  wheels,  operated  by  differential 
gear.  (See  Figs.  39  and  40.)  The  apparatus  is  inclined  from  the 
feed  to  the  discharge  end  at  a  slight  angle.  The  ore  to  be  roasted 
is  fed  in  mechanically  by  a  shoot,  and  travels  in  a  thin  layer  through 
each  of  the  revolving  tubes;  the  discharge  end  is  provided  with  a 
hood  with  suitable  openings,  through  which  the  ore  drops  con- 
tinuously into  a  hopper  beneath.  This  hood  opens  into  a  station- 
ary cylinder  of  steel  plate  which  conveys  the  heated  gases  directly 
from  the  fire-box  to  the  hood  and  thence  to  the  tubes.  The  fire- 
box is  mounted  on  wheels,  and  can  thus  be  easily  withdrawn  from 

1  Julian  and  Smart,  loc.  cit.,  p.  439. 


ROASTING  BEFORE  CYANIDE  TREATMENT 


289 


FIG.  38.  —  Merton  Furnace.     Plan  and  sectional  elevation. 
[From  drawing  furnished  by  Fraser  &  Chalmers.] 


290 


THE  CYANIDE   HANDBOOK 


ROASTING   BEFORE  CYANIDE  TREATMENT  291 


292  THE  CYANIDE  HANDBOOK 

the  furnace  if  necessary.  The  layer  of  ore  in  the  tubes  gradually 
diminishes  from  the  feed  to  the  discharge  end,  so  that  it  is  thinnest 
where  exposed  to  the  greatest  heat.  It  is  claimed  that  this 
furnace  gives  a  practically  perfect  roast,  with  less  dust  than  other 
furnaces  and  small  expense  for  repairs.  The  accompanying 
illustrations  are  furnished  by  the  Cyanide  Plant  Supply  Company. 
In  all  processes  of  treating  roasted  ore  with  cyanide,  it  is 
advisable  to  cool  the  ore  before  charging  into  the  treatment 
tanks.  This  is  done  sometimes  by  spreading  on  special  cooling 
floors.  In  other  cases  the  ore  is  sufficiently  cool  as  it  is  discharged 
from  the  conveyors  to  be  fed  direct  into  a  vessel  or  launder  con- 
taining the  cyanide  solution.  If  the  ore  is  sufficiently  hot  to 
raise  the  solution  to  boiling-point,  however,  a  very  large  con- 
sumption of  cyanide  takes  place,  and  the  extraction  is  ineffective, 
because  the  oxygen  is  thereby  expelled  from  the  solution. 


SECTION  IV 
USE  OF   AUXILIARY  DISSOLVING  AGENTS 

OXIDIZERS  IN  CONJUNCTION  WITH  CYANIDE 

As  soon  as  the  function  of  oxygen  in  the  reaction  taking  place 
between  gold  and  the  alkaline  cyanides  was  recognized,  the  sug- 
gestion of  adding  a  reagent  to  supply  the  necessary  oxygen  in  an 
active  and  concentrated  form  naturally  occurred  to  many  in- 
vestigators. A  very  large  number  of  substances  have  been  tried 
experimentally,  and  many  processes  involving  their  use  have  been 
suggested  and  patented;  but  the  only  oxidizers  which  appear  to 
have  had  even  a  limited  application  in  practice  are:  (1)  At- 
mospheric air,  injected  under  pressure  into  the  pulp  or  solution, 
or  beneath  the  filter-cloth;  (2)  sodium  peroxide;  (3)  potassium 
permanganate;  (4)  manganese  dioxide.  Other  substances,  such 
as  potassium  ferricyanide,  have  been  used,  which,  although  not, 
strictly  speaking,  oxidizers,  may  aid  the  reaction  by  liberating 
cyanogen  in  an  active  form. 

Oxidizers  act  in  two  ways:  by  supplying  oxygen  in  a  nascent 
or  active  condition,  so  accelerating  the  solution  of  gold;  by  oxidiz- 
ing deleterious  impurities  that  may  be  present  in  the  ore  or  solu- 
tion. The  general  conclusion  arrived  at  by  many  experimenters 
in  this  direction  is  that,  with  a  given  ore  crushed  to  a  given  degree 
of  fineness,  the  ultimate  maximum  extraction  of  gold  which  can 
be  attained  is  the  same,  whether  an  oxidizer  be  employed  or  not. 
The  only  advantage  secured  by  the  addition  of  the  oxidizer  is 
greater  rapidity  of  extraction.  In  practice,  this  advantage  is 
frequently  nullified  by  the  fact  that  much  time  is  necessarily 
consumed  in  washing  out  the  dissolved  gold,  and  as  this  washing 
is  done,  as  a  rule,  with  cyanide  solution,  the  dissolving  process 
is  carried  to  its  limit  in  either  case. 

Sodium  peroxide  has  been  used  to  some  extent  in  America 
in  connection  with  the  so-called  Kendall  process.  The  reagent  is 

293 


294  THE  CYANIDE  HANDBOOK 

generally  mixed  with  dry-crushed  ore  previous  to  cyanide  treat- 
ment. It  gives  up  its  oxygen  very  rapidly  in  contact  with  water; 
hence,  if  mixed  with  the  moist  ore  or  tailings  previous  to  or  during 
the  process  of  charging  into  the  vat,  the  oxygen  will  be  liberated 
and  the  greater  part  of  its  efficiency  lost  before  the  cyanide  solu- 
tion has  come  in  contact  with  the  ore. 

Potassium  permanganate  has  been  occasionally  used  in  South 
Africa  in  the  form  of  a  preliminary  wash,  especially  in  the  treat- 
ment of  concentrates.  It  should,  however,  be  removed  by  water- 
washing  previous  to  cyanide  treatment,  as  any  excess  remaining 
reacts  with  and  destroys  the  cyanide.  In  some  instances  a  mix- 
ture of  permanganate  and  sulphuric  acid  has  been  used  for  the 
preliminary  oxidation  and  removal  of  cyanicides. 

Manganese  dioxide  may  be  added  with  advantage  in  some  cases. 
It  gives  up  oxygen  gradually,  and  thus  the  beneficial  effect  is 
continued  throughout  the  treatment.1  In  this  respect  manganese 
dioxide  is  superior  to  sodium  peroxide  and  similar  reagents,  but 
if  used  in  excessive  amounts  it  causes  large  loss  of  cyanide,  and 
may  also  give  rise  to  objectionable  deposits  in  the  zinc-boxes. 

The  use  of  potassium  ferricyanide  in  conjunction  with  cyanide 
was  suggested  by  C.  Moldenhauer  in  1892.  It  is  not  in  reality 
an  oxidizing  agent,  but  reacts  by  liberating  a  part  of  cyanogen 
from  the  cyanide  and  forming  potassium  ferrocyanide 

KsFeCyo  +  KCy  =  K4FeCy6  +  Cy 
Au  +  Cy  +  KCy  =  KAuCy2. 

It  thus,  theoretically  at  least,  enables  the  cyanide  to  dissolve 
gold  in  the  absence  of  oxygen.  The  reaction  is  very  rapid  and 
effective,  but  other  secondary  reactions  occur  which  give  rise  to 
an  accumulation  of  salts  in  the  solution  and  deposits  in  the  zinc- 
boxes,  both  of  which  are  detrimental. 

Quantities  of  Oxidizers  to  be  Added.  —  No  definite  rule  can  be 
given  as  to  the  amounts  required,  as  this  will  depend  on  the  gold 
or  silver  value  of  the  material  to  be  treated  and  on  the  nature  and 
amount  of  the  oxidizable  materials  present.  In  all  cases  small- 
scale  preliminary  experiments  with  varying  quantities  should 
be  made,  and  the  effect  on  precipitation  tested  as  well  as  on  extrac- 
tion. 

1  As  is  well  known,  compounds  of  manganese  exhibit  a  tendency  to  act  as  "  car- 
riers "  of  oxygen,  by  alternately  combining  with  this  element  and  giving  it  up  to 
any  substance  capable  of  absorbing  it. 


USE   OF  AUXILIARY  DISSOLVING   AGENTS  295 

THE  BROMOCYANIDE  PROCESS 

An  auxiliary  agent  which  for  several  years  was  in  extensive 
and  successful  use  was  introduced  in  1894  by  Sulman  and  Teed. 
This  consists  of  the  bromide  of  cyanogen,  BrCy.  Other  haloid 
compounds  of  cyanogen  have  been  proposed,  and  their  use  was 
claimed  in  the  Sulman-Teed  patents,  but  they  have  never  been 
successfully  applied  in  practice.  The  reagent  is  a  volatile  crystal- 
line solid,  soluble  in  water,  and  when  mixed  with  an  alkaline 
cyanide  forms  a  very  powerful  and  rapid  solvent  for  gold.  Its 
action  is  discussed  in  Part  II,  but  it  may  be  repeated  here  that 
the  reaction  of  bromide  of  cyanogen  on  alkaline  cyanides  is  accom- 
panied by  the  evolution  of  cyanogen  or  hydrocyanic  acid,  and  that 
in  presence  of  an  excess  of  alkali  the  bromide  of  cyanogen  is 
immediately  destroyed  with  formation  of  bromide,  cyanate,  and 
(probably)  bromate  of  the  alkali  metal.  It  must  therefore  be 
used  in  solution  containing  little  or  no  free  alkali,  and  is  most 
effective  if  added  in  small  quantities  at  a  time.  The  bromide  of 
cyanogen  is  not  per  se  a  solvent  of  gold.  The  simplest  theory 
of  the  reaction  is  represented  thus: 

KCy  +  BrCy  =  KBr  +  Cy2. 

Au  +  KCy  +  Cy  =  KAuCy2 

BROMOCYANIDE  PRACTICE  IN  WESTERN  AUSTRALIA 

The  chief  centers  in  which  the  bromocyanide  process  has  been 
applied  are  the  Deloro  mine,  Ontario,  Canada,  where  a  mispickel 
ore  was  treated  without  roasting,  and  at  various  mines  in  the 
Kalgurli  district,  Western  Australia,  where  it  was  introduced  in 
conjunction  with  tube  milling,  or  fine  grinding  in  pans,  under  the 
name  of  the  Diehl  process. 

Details  of  the  process  will  be  found  in  the  following  papers: 
"The  Sulman-Teed  Gold  Extraction  Process,"  Sulman  and  Teed, 
in  "Journ.  Soc.  Chem.  Ind.,"  XVI,  961  (1897);  "The  Diehl 
Cyanide  Process,"  by  H.  Knutsen,  in  "Trans.  I.  M.  M.,"  XII,  2 
(1902);  "Metallurgy  of  the  Kalgoorlie  Goldfield,"  by  Gerard  W. 
Williams,  in  "Eng.  and  Min.  Journ.,"  LXXXV,  345  (Feb.  15, 1908). 
The  following  particulars  are  summarized  from  these  publications. 

The  ores  to  which  the  process  is  applied  in  Western  Australia 
are  sulpho-tellurides,  the  gold  in  which  cannot  be  extracted  by 
treating  raw  with  ordinary  cyanide  solutions.  In  the  Diehl 


296  THE  CYANIDE  HANDBOOK 

process  the  operations  are:  (1)  Crushing  and  grinding  to  a  high 
degree  of  fineness.  (2)  Treating  the  finely  ground  ore  by  agita- 
tion with  a  cyanide  solution,  to  which  bromide  of  cyanogen  is 
added  at  intervals.  (3)  Separating  solution  from  sludge  by  means 
of  filter-presses.  (4)  Precipitation  on  zinc  shavings.  In  some 
plants  amalgamation  and  concentration  are  used,  the  concentrates 
being  generally  roasted  and  treated  by  ordinary  cyanide. 

The  grinding  is  done  in  Krupp  tube  mills,  18  ft.  long  by  4ft. 
diameter,  the  fine  sands  being  reground  until  the  whole  product 
passes  a  200-mesh  sieve,  less  than  3  per  cent,  remaining  on  220. 
The  slimes,  after  removal  of  excess  of  water  by  spitzkasten,  go 
to  agitators,  where  they  are  treated  first  with  ordinary  cyanide. 
The  dilution  of  pulp  is  about  2  parts  ore  to  3  of  water.  Cyanide 
is  added  in  quantity  sufficient  to  form  a  solution  of  0.10  per  cent. 
KCy,  equivalent  to  0.15  parts  KCy  per  100  parts  of  dry  slime. 
After  from  one  and  a  half  to  two  hours'  agitation  with  cyanide 
alone,  the  bro'mocyanide  is  added  in  the  proportion  of  0.04  parts 
per  100  parts  of  dry  slime,  equivalent  to  a  strength  of  about 
0.027  per  cent.  BrCy  in  the  solution.  This  mixture  is  agitated 
for  twenty-four  hours,  lime  being  added  two  hours  before  the 
finish  in  the  proportion  of  3  to  4  Ib.  per  ton  of  dry  ore.  The 
sludge  is  then  run  into  a  receiver,  from  which  it  is  forced  by  com- 
pressed air  into  the  filter-presses. 

The  above  details  refer  to  the  treatment  at  Hannan's  Star 
mill,  1902.  The  system  varies  slightly  at  different  plants,  but 
in  general  the  amount  of  bromocyanide  used  is  from  J  to  J  that 
of  the  cyanide,  corresponding  approximately  with  the  proportions 
indicated  by  the  equations  given  above. 

According  to  G.  W.  Williams  (loc.  ciL),  the  treatment  at  the 
mines  of  the  Ivanhoe  Gold  Corporation  is  as  follows:  After  con- 
centration on  Wilfley  tables,  the  sands  are  ground  in  pans,  recon- 
centrated,  the  fines  separated  by  spitzlutten  and  conveyed  to 
settlers.  The  slimes  after  settlement  are  pumped  to  agitators, 
where  they  are  diluted  with  weak  solution  to  form  a  pulp  with 
the  proportions  1:1,  dry  ore  to  solution.  After  two  hours'  agi- 
tation, 0.6  Ib.  bromocyanide  is  added  per  ton  of  dry  slimes  and 
the  agitation  continued  for  twelve  hours.  Lime  is  then  added  in 
the  proportion  of  1  Ib.  per  ton  of  dry  slimes.  The  pulp  is  then 
filter-pressed.  The  agitators  are  20  ft.  in  diameter  by  8  ft.  deep, 
closed  in  and  fitted  with  mechanical  stirring  gear.  The  method 


USE   OF  AUXILIARY  DISSOLVING  AGENTS  297 

involves  a  separate  treatment  of  the  concentrates,  which  amount 
to  18  per  cent,  of  the  total  tonnage.  These  are  roasted  in  Edwards 
furnaces,  mixed  with  spent  cyanide  solution,  ground  fine  in  pans, 
agitated  with  0.1  per  cent,  cyanide  and  filter-pressed.  The  entire 
scheme  of  treatment  comprises 

Recovery:  per  cent 
of  total  gold. 

Amalgamation    28 

Treatment  of  concentrates  by  roasting  and  ordinary  cyanide     ....  13 

Treatment  of  sands:  5  days  percolation   17.5 

Treatment  of  slimes  by  bromocyanide 28 

Total  recovery 86.5 

The  total  treatment  cost  is  given  as  $2.20  per  ton.  The  recovery 
by  similar  systems  of  treatment  in  other  plants  varies  from  85 
to  95  per  cent.  Other  plants  treating  a  portion  of  their  product 
by  bromocyanide  are  the  Golden  Horseshoe,  Oroya-Brownhill, 
and  Lake  View  Consols. 

Owing  to  the  instability  of  the  reagent  and  the  unpleasantness 
of  handling  it  in  quantity,  mixtures  of  various  salts  are  prepared 
and  shipped  to  the  mines,  which,  on  addition  to  the  cyanide  solu- 
tion, produce  bromo-cyanide  in  the  required  proportion,  for 
instance,  a  mixture  of  cyanide,  bromide,  bromate,  and  bisulphate 
of  sodium. 

USE  OF  MERCURIC  CHLORIDE 

Keith  and  Hood  have  proposed  the  addition  of  mercuric 
chloride  or  of  a  double  cyanide  of  mercury  to  the  solution.  It  is 
found  that  the  action  of  the  cyanide  on  gold,  and  still  more  on 
silver,  is  greatly  accelerated.  This  reagent  is  occasionally  em- 
ployed as  an  auxiliary  to  cyanide  in  the  treatment  of  ores  con- 
taining silver  as  sulphide.  The  presence  of  small  amounts  of 
mercury  in  the  solution  is  also  beneficial  in  assisting  the  pre^ 
cipitation  of  the  precious  metals  in  the  zinc-boxes.  The  solvent 
effect  on  sulphide  ores  is  apparently  due  to  the  great  affinity  of 
mercury  for  sulphur,  and  may  be  represented  thus: 

Ag2S  =  HgS  +  2KAgCy2 


SECTION   V 

ELECTROLYTIC   PRECIPITATION   PROCESSES 

THE  idea  of  using  an  electric  current  for  precipitating  the  pre- 
cious metals  from  their  cyanide  solutions  dates  at  least  as  far  back 
as  1840,  when  Elkington's  patent  for  electroplating  and  electro- 
gilding  was  taken  out  (E.  P.  No.  8447;  Sept.  25,  1840).  In  fact, 
the  supposition  that  an  electric  current  was  necessary,  at  least 
for  the  precipitation  if  not  for  the  solution  of  metals  in  cyanide, 
appears  to  have  been  general  among  investigators  up  to  the  time 
of  the  discovery  of  zinc-thread  precipitation. 

THE  SIEMENS-HALSKE  PROCESS 

About  the  year  1887  the  firm  of  Siemens  and  Halske,  of 
Berlin,  introduced  an  electrolytic  process  for  depositing  copper, 
zinc,  gold,  silver,  etc.,  from  cyanide  solutions.  (See  E.  P.  No. 
-3533;  Feb.  27,  1889.)  This  process  was  subsequently  applied 
to  the  treatment  of  solutions  resulting  from  the  cyanide  extrac- 
tion of  gold  ores  and  tailings,  and  for  several  years  found  an 
extensive  application  in  South  Africa,  where  it  was  introduced 
by  A.  von  Gernet  in  1893. 

In  its  original  form,  this  process  consisted  in  precipitating 
the  metals  from  cyanide  solutions  by  means  of  an  electric  current 
passed  between  anodes  of  iron  and  cathodes  of  sheet  lead,  the 
precious  metals  being  deposited  on  the  latter,  while  the  iron  was 
gradually  converted  into  oxide,  and  ultimately  into  soluble  and 
insoluble  cyanogen  compounds,  such  as  ferrocyanides.  Some 
account  of  the  introduction  and  working  of  the  process  at  the  plant 
of  the  Worcester  mine,  Johannesburg,  where  it  was  first  applied 
in  South  Africa  on  a  working  scale,  is  given  by  von  Gernet.1  The 
method  of  applying  this  process  usually  adopted  in  South  Africa 
was  to  place  the  anode  and  cathode  plates  in  the  compartments 
of  a  box  similar  to  the  ordinary  zinc-box,  but  of  larger  dimensions, 
so  as  to  allow  from  15  to  25  cu.  ft.  per  ton  of  solution  per  24  hours. 

i "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  S.  A."  I,  28  (Aug.  18,  1894). 

298 


ELECTROLYTIC   PRECIPITATION  PROCESSES  299 

The  plates  were  commonly  arranged  parallel  to  the  sides  of  the 
box;  in  each  compartment  the  anodes  and  cathodes  were  placed 
alternately  side  by  side,  the  cathodes  of  one  compartment  being 
connected  electrically  with  the  anodes  of  the  next  lower  com- 
partment. The  anodes  of  the  top  compartment  were  connected 
with  the  positive  pole  of  a  battery,  dynamo,  or  other  source  of 
current,  the  cathodes  of  the  bottom  compartment  being  connected 
with  the  negative  pole  of  the  same. 

The  anodes  were  rectangular  plates  of  sheet  iron,  J  to  J  in. 
thick,  with  an  effective  area  of,  say,  5  sq.  ft.  They  were  usually 
held  in  grooves  or  by  means  of  slats  at  the  sides  of  the  box,  and 
were  enclosed  in  canvas  bags  to  insulate  them  from  the  cathodes 
and  to  collect  the  products  of  the  reaction  (ferric  oxide,  etc.) 
referred  to  above. 

The  cathodes  were  of  thin  sheet  lead  suspended  on  horizontal 
wires  between  each  pair  of  anodes,  at  about  3-in.  distances.  As 
it  was  found  advantageous  to  increase  the  cathode  area  as  much 
as  possible,  in  later  practice  the  lead  sheets  were  cut  into  long 
strips  and  the  threads  separated  as  much  as  possible  so  as  to  give 
the  maximum  surface  for  precipitation.  A  current  of  .04  ampere 
per  sq.  ft.  of  anode  surface  was  usually  sufficient,  and  was  found 
to  deposit  the  gold  on  the  cathodes  in  a  coherent  form.  When 
sufficiently  coated  with  precious  metal,  the  cathodes  were  removed 
and  replaced  by  fresh  ones,  without  interrupting  the  regular 
working  of  the  box;  they  were  then  melted  in  a  reverberatory 
furnace  and  cast  into  lead-bullion  bars.  These  were  then  cupeled 
in  an  ordinary  cupeling  furnace.  A  part  of  the  lead  was  recovered 
for  re-use  by  reduction  of  the  litharge  resulting  from  the  latter 
operation.  A  further  quantity  of  gold  was  obtained  by  treating 
the  sludge  which  formed  inside  the  sacks  containing  the  anodes. 

The  chief  advantages  claimed  for  the  Siemens-Halske  process 
were:  (1)  The  possibility  of  precipitating  gold. from  solutions 
very  weak  in  cyanide,  which  did  not  admit  of  treatment  by  the 
ordinary  zinc  process.  It  was  thus  practicable  to  employ  only 
the  minimum  quantity  of  cyanide  needed  for  dissolving  the  gold. 
This  was  of  particular  importance  in  the  treatment  of  slimes  by 
the  decantation  process,  where  the  volume  of  liquid  used  per  ton 
of  material  treated  was  necessarily  large.  (2)  The  purity  of  the 
bullion  obtained  by  cupellation  of  the  lead  bars  as  compared  with 
that  produced  by  the  ordinary  smelting  of  zinc  precipitate. 


300  THE  CYANIDE  HANDBOOK 

(3)  There  was  no  necessity  for  interrupting  the  regular  work  of  the 
plant  during  the  clean-up.  (4)  Copper  and  other  obnoxious  base 
metals  were  removed  from  the  solution  very  effectively.  (5) 
There  was  no  accumulation  of  double  cyanide  of  zinc,  etc.,  in 
the  solution,  which  remained  always  in  good  working  condition 
and  did  not  become  charged  with  foreign  salts. 

On  the  other  hand  there  were  certain  evident  disadvantages: 
(1)  The  necessity,  when  dealing  with  solutions  low  in  gold  value, 
of  a  large  surface  for  deposition,  involving  the  use  of  boxes  of 
great  size,  and  hence  considerable  initial  outlay.  (2)  More  skill 
and  attention  was  needed  to  secure  satisfactory  working  than  with 
zinc  precipitation. 

With  the  introduction  of  the  zinc-lead  couple  in  1898,  the 
first  and  principal  advantage  of  the  Siemens-Halske  process  dis- 
appeared, as  it  was  then  found  possible  to  precipitate  effectively 
by  means  of  zinc  from  solutions  as  weak  in  cyanide  as  those  dealt 
with  by  the  electrolytic  process.  By  the  use  of  the  Tavener 
process  (see  Part  V),  or  by  various  methods  of  refining  zinc  pre- 
cipitate, as  for  example  by  fluxing  with  dioxide  of  manganese 
in  clay-lined  pots,  it  is  also  possible  to  obtain  bullion  from  the 
zinc  process  having  the  same  fineness  as  that  furnished  by  cupella- 
tion  in  the  Siemens-Halske  process. 

LATER  DEVELOPMENTS  OF  ELECTROLYTIC  PROCESS 

As  the  action  of  the  solution  on  the  anodes  gave  rise  to  a 
troublesome  by-product,  many  attempts  were  made  to  find  a 
material  for  the  anodes  which  would  be  insoluble  in  the  cyanide 
solution.  Thick  sheet  lead  was  used  for  some  time  by  Charles 
Butters,  but  this  had  a  tendency  to  become  hard  and  brittle, 
and  under  certain  conditions  became  rapidly  coated  with  cyanide 
of  lead,  so  that  after  use  for  a  short  time  the  plates  crumbled  to 
pieces.  E.  Andreoli  and  others  used  anodes  of  lead  coated  with 
a  layer  of  peroxide  of  lead;  this  was  obtained  by  immersing  the 
sheets  in  a  bath  of  potassium  permanganate  or  of  plumbate  of 
soda.  They  were  then  immersed  in  strong  cyanide  solution  and 
an  electric  current  passed  through,  which  caused  the  coating  of 
peroxide  to  become  firm  and  hard.  These  plates  were  practically 
insoluble  in  the  solution,  and  hence  no  by-products  were  formed. 
Many  attempts  were  also  made  to  find  a  cathode  from  which 
the  deposit  could  be  removed  as  required  without  destruction 


ELECTROLYTIC   PRECIPITATION   PROCESSES  301 

of  the  cathode  itself.  Sheet-iron  carefully  freed  from  oxide  has 
been  used;  the  gold  deposit  is  removed  by  immersing  the  cathode 
in  a  bath  of  molten  lead.  A  more  satisfactory  method,  however, 
is  to  use  a  cathode  of  tinned  iron.  This  was  applied  successfully 
at  Charles  Butters  and  Company's  works  at  Minas  Prietas,  Mexico, 
and  at  Virginia  City,  Nevada.  The  gold  and  silver  are  deposited 
in  a  loose  form,  so  that  they  may  be  rubbed  off  from  time  to  time, 
to  collect  as  a  sludge  at  the  bottom  of  the  box.  This  is  cleaned 
up  at  intervals  and  smelted  direct,  yielding  high-grade  bullion, 
while  the  cathode  remains  intact.  When  much  base  metal,  e.g., 
copper,  is  present  in  the  solution,  however,  there  is  a  dense  hard 
deposit  on  the  plates,  which  is  scraped  off  with  difficulty;  also  a 
considerable  amount  of  gold  adheres  to  the  plate  before  any  of  the 
deposit  begins  to  fall. off. 

ELECTROLYTIC  PROCESS  FOR  GOLD-COPPER  ORES 

The  following  system  of  combined  electrolytic  and  zinc  pre- 
cipitation was  used  by  C.  P.  Richmond,  at  the  San  Sebastian 
mine,  Salvador,  Central  America,1  for  the  treatment  of  a  complex 
ore  containing  copper,  arsenic,  antimony,  and  tellurium.  The 
ore  is  crushed  in  ball  mills  and  roasted.  The  sand  and  slime  are 
then  separated  in  cyanide  solution,  the  sand  being  treated  by 
percolation  and  the  slime  by  agitation  and  filter-pressing.  The 
greater  part  of  the  gold,  together  with  some  copper,  is  precipi- 
tated by  electrolysis,  after  which  the  solutions  are  passed  through 
a  zinc-box  to  recover  the  residual  gold.  The  accumulation  of 
copper  in  the  solution  is  thus  prevented. 

The  cyanide  solution,  averaging  16  dwt.  per  ton,  flows  through 
the  electric  box  at  the  rate  of  150  tons  per  24  hours;  the  box  is 
30  ft.  long  by  10  ft.  wide,  and  4  ft.  8  in.  deep,  and  is  inclined  1  in. 
per  foot.  There  are  twelve  compartments,  but  the  last  two  are 
used  for  settlement  only,  so  that  the  effective  capacity  is  1 166  cu. 
ft.,  or  about  8  cu.  ft.  per  ton  per  24  hours.  Each  compartment 
has  25  anodes  and  24  cathodes.  The  anodes  are  rolled  lead 
plates  22  X  48  X  J  in.  The  cathodes  are  lead  plates  of  similar 
size,  but  only  ^  in.  thick.  The  anodes  are  peroxidized  by 
immersing  them  in  a  solution  of  potassium  permanganate,  with 
or  without  sulphuric  acid.  One  method  is  to  dip  them  in  a  solu- 
tion of  1  per  cent.  KMnO4  and  2  per  cent.  H2SO4,  keeping  them 

i  Chas.  P.  Richmond,  "  E.  and  M.  J.,"  LXXXIII,  512. 


302  THE  CYANIDE  HANDBOOK 

for  six  hours  under  a  current  of  2.5  amperes  per  square  foot.  By 
this  means  a  coating  of  lead  peroxide  is  obtained  which  lasts  8  to 
12  months. 

In  the  boxes,  the  anodes  and  cathodes  of  successive  compart- 
ments are  connected  in  series,  with  a  current  strength  of  1  ampere 
per  square  foot.  The  gold  and  copper  form  a  hard  dense  coating 
on  the  cathodes,  with  no  tendency  to  fall  off  as  sludge,  but  there 
is  a  gradual  accumulation  of  low-grade  precipitate  on  the  anodes 
and  at  the  bottom  of  the  box.  After  passing  the  electric  box, 
the  solution  flows  through  two  zinc-boxes  22  ft.  long,  with  fourteen 
compartments,  each  2  X  2  X  1  ft.,  which  reduces  the  gold  con- 
tents to  about  0.06  to  0.10  dwt.  per  ton.  Hardly  any  copper  is 
deposited  in  the  zinc-box.  The  electrical  box  precipitates  80  to  90 
per  cent,  of  the  gold,  together  with  much  copper,  which  is  then 
separated  as  follows:  After  remaining  in  the  cyanide  electric  box 
for  20  to  30  days;  the  cathodes  are  transferred  to  another  box, 
where  they  are  used  as  anodes.  This  box  contains  sulphuric  acid 
of  2  to  3  per  cent.  H2SO4,  the  cathodes  used  being  lead  plates 
TV  in.  thick.  There  are  four  compartments,  each  containing  5 
anodes  and  6  cathodes,  4  in.  apart  and  connected  in  series.  The 
current  used  is  5  amperes  per  square  foot  of  anode  surface.  The 
anodes  are  hung  in  a  wooden  frame  with  closed  bottom  and  open 
sides,  over  which  is  stretched  a  sack  of  cotton  cloth.  The  copper 
dissolves  and  precipitates  on  the  cathodes,  where  it  forms  a  slime, 
which  falls  to  the  bottom.  The  gold  remains  in  a  loose  form  in 
the  anode  sacks.  The  anode  plates  are  then  washed  and  returned, 
as  cathodes,  to  the  cyanide  electric  box.  Special  arrangements 
are  employed  to  secure  circulation  of  the  acid  liquid  and  to  pre- 
vent short-circuiting. 

To  recover  the  gold,  the  acid  liquid  is  syphoned  off,  and  the 
anode  frames  are  raised  and  allowed  to  drain  over  the  box.  They 
are  then  suspended  over  a  filter-tank,  the  sacking  at  the  sides  is 
cut  away,  and  the  gold  precipitate  washed  into  the  tank.  The 
frames  and  old  sacks  are  washed  in  the  same  tank.  When  thor- 
oughly drained,  the  precipitate  is  removed  from  the  tank,  dried, 
and  smelted  in  graphite  pots.  The  copper  slime  from  the  cathodes 
is  flushed  through  holes  near  the  bottom  of  the  box,  filtered,  and 
dried.  The  bullion  recovered  is  high-grade,  and  owing  to  the 
constant  precipitation  of  copper  there  is  a  regeneration  of  cyanide 
amounting  to  30,000  Ib.  in  a  year's  run.  Sufficient  copper  is 


ELECTROLYTIC   PRECIPITATION  PROCESSES  303 

extracted  to  cover  the  cost  of  refining  by  the  acid  box  and  smelt- 
ing of  gold  precipitate. 

OTHER  ELECTROLYTIC  PROCESSES 

Numerous  processes  have  been  suggested  and  tried  experi- 
mentally, but  very  few  have  achieved  even  a  temporary  com- 
mercial success.  In  the  so-called  "  electro-zinc "  process,  zinc 
plates  were  used  as  anodes,  and  amalgamated  zinc  or  copper 
plates  as  cathodes.  The  anode  being  soluble,  a  smaller  current 
could  be  used  than  with  insoluble  or  slightly  soluble  anodes,  but 
the  method  was  unsatisfactory  owing  to  the  rapid  accumulation 
of  zinc  ferrocyanide.  The  effect  of  the  current  is  also  to  produce 
a  hard  non-adherent  amalgam.  Many  attempts  have  been  made 
to  use  carbon  as  anode,  but  it  is  difficult  to  obtain  it  in  a  form 
which  will  not  disintegrate  under  the  current.  Aluminium  has 
been  used  as  cathode  by  S.  Cowper  Coles,  but  there  appears  to  be 
much  difficulty  in  removing  the  precipitated  gold.  Mercury  is 
not  suitable  as  a  cathode,  for  the  reason  pointed  out  by  von 
Gernet,  that  it  is  not  practicable  to  obtain  the  enormous  area 
required  for  effective  precipitation  of  solutions  low  in  gold. 
Amalgamated  copper  plates  have,  however,  been  frequently 
tried,  and  an  interesting  series  of  experiments  with  them  has 
been  made  by  T.  K.  Rose.1  These  experiments  show  that  with 
solutions  rich  in  gold,  a  current  of  0.03  amperes  per  square  foot 
precipitates  the  gold  as  a  black  powder  which  does  not  amal- 
gamate. Other  objections  arise  from  the  cost  of  the  process, 
the  fact  that  the  plates  absorb  a  portion  of  the  gold,  and  that 
they  are  corroded  by  the  action  of  the  current. 

Douglas  Lay2  enumerates  several  drawbacks  inherent  to 
electrocyanide  processes  in  general.  A  very  weak  current  must 
necessarily  be  used,  to  avoid  excessive  action  on  the  anodes; 
this  in  turn  involves,  as  already  pointed  out,  a  very  large 
cathode  area  when  solutions  low  in  gold  are  to  be  treated.  He 
also  states  that  deposition  of  carbonate  of  lime  on  the  cathodes 
takes  place,  involving  a  decomposition  of  cyanide  and  so  coating 
the  cathodes  as  to  prevent  precipitation  of  the  precious  metals. 

!" Trans.  I.  M.  and  M.,"  VIII,  369. 
*"E.  and  M.  J.,"  April  11,  1908,  p.  765. 


304  THE  CYANIDE  HANDBOOK 

SOLUTION  AND  ELECTROLYTIC  PRECIPITATION  IN  THE 
SAME  VESSEL 

The  idea  of  dissolving  and  precipitating  the  gold  simultaneously 
in  one  and  the  same  tank  or  receiver  is  an  old  and  favorite  one 
with  inventors;  it  figures  in  J.  H.  Rae's  apparatus,  patented  in 
1867,  and  reappears  in  various  forms  in  the  Pelatan-Clerici, 
Riecken,  Gilmour- Young  and  other  processes,  in  which  an  electric 
current  also  is  generally  introduced,  as  an  aid  both  to  solution 
and  precipitation.  There  appears,  however,  to  be  very  little 
evidence  that  the  electric  current  aids  the  solution  of  the  precious 
metals  in  any  way,  and  with  regard  to  precipitation  it  is  for 
various  reasons  more  effective  in  solutions  from  which  the  sus- 
pended solid  matter  has  been  removed. 

In  the  Pelatan-Clerici  process,  used  at  Delamar,  Idaho,  in 
1897,  the  pulp  was  agitated  with  cyanide  solution  in  vats,  the 
bottoms  of  which  were  composed  of  sheet-copper,  covered  with 
mercury,  and  constituting  the  cathodes.  The  anodes  were  in 
the  form  of  sheet-iron  agitators,  so  that  the  gold  could  be  dis- 
solved and  precipitated  in  the  same  vessel.  The  gold  was  re- 
covered in  the  form  of  amalgam. 

The  Riecken  process  was  introduced  at  South  Kalgurli;  Western 
Australia,  in  1900.  The  ore  is  roasted,  mixed  to  a  thick  pulp 
with  cyanide  solution,  and  fed  to  agitation  vats,  of  about  13 
tons  capacity,  having  vertical  ends  and  sloping  sides.  The  latter 
are  provided  with  amalgamated  copper  plates,  over  which  a  thin 
stream  of  mercury  constantly  flows.  The  coarse  gold  amalgamates 
directly.  An  electric  current  is  passed  through  the  vat  by  means 
of  iron  rods,  which  constitute  the  anodes,  the  amalgamated  plates 
forming  the  cathodes.  The  current  used  is  150  amperes  at  1.5 
volts,  with  a  density  of  0.4  ampere  per  square  foot.  A  charge  of 
13  tons  can  be  treated  in  18  hours  with  an  extraction  of  93 
per  cent,  from  ore  assaying  over  an  ounce  per  ton.  The  cost, 
exclusive  of  crushing  and  roasting,  is  given  as  9  s.  4.8  d.  per 
ton.1 

In  the  Molloy  process  the  cathode  consisted  of  mercury,  and 
the  anode  of  peroxidized  lead  immersed  in  sodium  carbonate, 
contained  in  a  compartment  which  separated  it  from  the  cyanide 

*  T.  K.  Rose,  "  Metallurgy  of  Gold,"  4th  edition,  p.  346. 


ELECTROLYTIC   PRECIPITATION   PROCESSES  305 

solution.  The  result  of  the  electrolysis  was  to  form  sodium 
amalgam  which  permeated  the  mercury  in  the  outer  vessel.  The 
gold  was  precipitated  and  amalgamated,  with  regeneration  of 
cyanide,  thus: 

Na  +  KAuCy2  =  Au  +  KCy  +  NaCy 


SECTION   VI 

OTHER   PRECIPITATION   PROCESSES 

IN  this  section  we  propose  to  give  a  brief  description  of  various 
processes  not  involving  the  use  of  an  electric  current,  which  have 
been  proposed  as  alternatives  to  the  ordinary  method  of  zinc  pre- 
cipitation. These*  may  be  classified  as  follows:  (1)  Methods  in 
which  the  values  are  dissolved  and  amalgamated  in  the  same 
vessel.  (2)  Precipitation  with  finely  divided  zinc  (dust  or  fume). 
(3)  Precipitation  with  charcoal.  (4)  Precipitation  with  cuprous 
salt  in  acid  solution. 

The  Gilmour-Young  process,  employed  at  the  Santa  Francisca 
mine,  Nicaragua,  consists  in  agitating  the  gold-bearing  material, 
which  contains  much  clay,  as  a  thick  pulp,  in  pans,  with  addition 
of  mercury  and  cyanide.  After  two  hours  of  this  treatment, 
copper  and  zinc  amalgam  are  added  and  the  pan  run  for  four 
hours  longer.  Thus  the  same  vessel  is  used  for  solution  and 
precipitation.  The  gold  and  silver  are  obtained  as  amalgam,  which 
is  separated  and  retorted  in  the  usual  way.  Extraction  of  80  to 
90  per  cent,  of  the  gold  is  said  to  have  been  obtained.  For 
details  see  "Min.  Ind.,"  VII,  334.1 

Zinc-dust  Precipitation.  —  This  method  was  originally  applied 
by  H.  L.  Sulman 2  and  H.  K.  Picard,  at  the  Deloro  mine,  Ontario, 
Canada.  It  has  been  extensively  used  in  the  United  States, 
notably  at  Mercur,  Utah,  and  in  the  Black  Hills,  South  Dakota. 
The  zinc-dust  consists  of  the  finely  divided  metal  obtained  by 
the  distillation  and  condensation  of  zinc,  and  generally  contains 
about  90  per  cent,  of  metallic  zinc.  A  small  amount  of  lead  is 
usually  present,  which  is  advantageous  for  precipitation.  The 
zinc  is  very  finely  divided,  over  95  per  cent,  of  the  powder  passing 
a  200-mesh  sieve.  In  this  condition  it  is  very  easily  oxidized,  and 
Sulman  has  proposed  the  use  of  ammonia  and  ammonium  salts 
for  dissolving  the  oxide  and  cleansing  the  surface  previous  to  use. 

lAlso,  "Trans.,  I.  M.  and  M."  Nov.  16,  1898. 
2Eng.  Patents  Nos.  18003  and  18146,  1894. 
306 


OTHER   PRECIPITATION   PROCESSES  307 

The  following  description  of  the  use  of  this  reagent  is  given 
by  W.  J.  Sharwood.1  The  solution  to  be  precipitated  is  run  into 
a  collecting  tank  and  agitated  for  a  few  minutes.  A  suitable 
quantity  of  the  dust  is  then  introduced,  which  may  be  sprayed 
into  the  tank  as  an  emulsion.  The  mixture  is  then  forced  by  a 
pump  through  a  filter-press,  from  which  the  barren  liquid  flows 
to  the  storage  tanks,  the  precipitated  metals  and  any  excess  of 
zinc  remaining  in  the  press.  These  form  a  porous  mass  which 
offers  slight  resistance  to  the  passage  of  solution.  The  extra 
power  required,  as  compared  with  zinc-thread  precipitation,  is 
slight,  but  some  trouble  is  experienced,  owing  to  the  clogging  of 
the  filter-cloths  when  the  solutions  are  turbid  with  suspended 
siliceous  matter.  From  J  to  J  Ib.  of  zinc-dust  is  used  per  ton  of 
solution  treated.  About  6  tons  of  liquid  per  hour  can  be  passed 
through  every  100  sq.  ft.  of  filter-cloth  in  the  press.  When  a 
clean-up  is  to  be  made,  the  contents  of  the  press  are  washed  by 
pumping  a  little  water,  then  partially  dried  by  forcing  air  through 
it.  When  the  press  is  opened  and  the  frames  shaken,  the  cakes 
fall  out  readily.  At  this  stage,  the  product  usually  carries  about 
one-third  of  its  weight  of  water;  its  composition  does  not  differ 
materially  from  that  of  the  precipitate  obtained  with  zinc  sha- 
vings, and  it  may  be  treated  in  the  same  way.  It  is,  however, 
more  uniform,  owing  to  the  absence  of  threads  of  "short  zinc." 
The  blowing  operation  oxidizes  some  of  the  zinc  and  sometimes 
causes  the  presses  to  become  warm.  The  evolution  of  hydrogen 
which  accompanies  precipitation  continues  slowly  while  the 
moist  precipitate  remains  in  the  press.  Care  must  therefore 
be  taken  to  bring  no  naked  lights  near  while  the  clean-up  is 
proceeding. 

One  filter-press,  with  16  frames  2  ft.  square,  working  15  to 
16  hours  per  day,  requires  2  h.p.  (neglecting  the  additional  fric- 
tion in  pumps)  in  excess  of  the  power  required  for  pumping  when 
zinc  shavings  are  used.  In  other  cases,  however,  difficulties  have 
been  experienced  in  treating  the  precipitate  after  removal  from 
the  presses.  It  was  found  to  pack  so  hard  that  it  was  difficult 
to  disintegrate  it  for  the  acid  treatment,  so  that  it  was  practically 
impossible  to  dissolve  the  zinc  in  dilute  sulphuric  acid.  The 
particles  are  said  to  become  coated  with  a  thin  layer  of  metallic 

i  "  E.  and  M.  J.,"  LXXIX,  752  (from  13th  annual  convention  California  Miners' 
Assoc.,  December,  1904). 


308  THE  CYANIDE   HANDBOOK 

gold  which  protects  them  from  the  acid,  but  a  mixture  of  nitric 
and  sulphuric  acids  has  been  found  to  be  effective.1 

The  precipitation  by  zinc-dust  or  fume  appears  to  be  rapid 
and  complete,  five  minutes'  agitation  being  sometimes  sufficient 
for  the  reaction;  but  the  difficulties  in  collecting  and  refining  the 
precipitate  have  led  to  the  abandonment  of  the  process  in  several 
cases  where  it  had  been  originally  adopted,  e.g.,  at  various  plants 
in  the  Black  Hills.  Much  ingenuity  has  been  exercised  in  devising 
apparatus  for  mixing  the  zinc  effectively  with  the  solution,  and 
for  settling  the  precipitate  after  mixture.  Picard  used  a  conical 
vessel,  in  which  the  fume  was  fed  in  through  a  central  funnel  and 
met  an  ascending  current  of  solution  which  was  passed  through 
a  perforated  conical  distributor  near  the  bottom  of  the  cone. 
The  settler  contained  a  number  of  transverse  plates  of  glass  or 
smooth  wood,  set  at  an  angle  of  45°,  on  which  any  particles  not 
collected  in  the  cone  are  deposited.2 

.  Charcoal  Precipitation.  —  The  fact  that  gold  is  precipitated 
by  charcoal  from  cyanide  solutions  has  long  been  known,  though 
no  satisfactory  explanation  of  the  reaction  has  yet  been  given. 
It  has  been  alleged  to  be  due  to  occluded  hydrogen  or  hydro- 
carbons contained  in  the  pores  of  the  charcoal.  The  method  has 
been  used  in  several  small  plants  in  Victoria,  Australia,  on  a 
working  scale.3  The  charcoal,  crushed  to  a  suitable  size,  is  placed 
in  tubs  about  2  ft.  in  diameter,  having  a  central  vertical  cylinder 
also  filled  with  charcoal.  These  are  used  much  in  the  same  way 
as  Caldecott's  vats  for  zinc  precipitation;  the  solution  passes 
downward  through  the  central  column  and  upward  in  the  outer 
portion,  the  overflow  passing  in  this  way  through  a  succession  of 
tubs  each  at  a  slightly  lower  level  than  the  last.  As  about 
24  Ib.  of  charcoal  are  required  for  the  precipitation  of  an  ounce 
of  gold,  the  quantity  needed  in  a  plant  of  any  size  would  be  very 
large.  To  recover  the  gold,  the  charcoal  is  burnt  to  ashes  in  a 
special  furnace  so  arranged  that  the  products  of  combustion  pass 
through  water,  to  avoid  mechanical  loss.  The  ash  is  then  smelted 
with  a  mixture  of  sand  and  borax.  According  to  experiments 
made  by  Prof.  S.  B.  Christy,  the  efficiency  of  the  charcoal  rapidly 
falls  off  with  continued  passage  of  the  solution. 

Precipitation  with  Cuprous  Salts.  —  This  method  seems  to  have 

i  "  Min.  Sci.  Press./*  XCIIT,  607  (Nov.  17,  1906). 

2 "Trans.  Fed.  Inst.  Min.  Eng.,"  XV,  417. 

»  J.  T.  Lowles,  "  Trans.  I.  M.  and  M.,"  VII,  192. 


OTHER  PRECIPITATION   PROCESSES  309 

been  suggested  independently,  about  1895,  by  Prof.  P.  de  Wilde, 
of  Brussels,  and  Prof.  S.  B.  Christy,  of  Berkeley,  California.  It 
depends  on  the  fact  that  gold  is  precipitated  completely  as  aurous 
cyanide  on  acidifying  the  cyanide  solution  and  adding  a  sufficient 
excess  of  a  cuprous  salt.  Several  modifications  have  been  pro- 
posed, in  which  an  attempt  is  made  to  regenerate  the  cyanide 
decomposed  in  the  reaction,  or  to  precipitate  the  cyanogen  in 
some  form  from  which  a  soluble  cyanide  may  subsequently  be 
recovered  before  precipitating  the  gold.  It  is  obvious,  however, 
that  a  method  involving  the  acidification,  or  at  least  the  neutraliza- 
tion, of  100  tons  or  more  of  alkaline  liquor  per  day  is  hardly  likely 
to  find  a  practical  application.  The  precipitants  suggested  are: 

(1)  a  mixture  of  copper  sulphate  and  sulphurous  acid  (De  Wilde); 

(2)  freshly  precipitated   cuprous   sulphide,   to   be   agitated  with 
the  solution  (Christy);  (3)  cuprous  chloride  dissolved  in  common 
salt.     After  calcining  the  precipitate,  the  oxide  of  copper  is  fco  be 
removed  by  dissolving  in  sulphuric   acid,   leaving  nearly  pure 
gold.     The  method  forms  the  basis  of  the  analytical  methods 
for  determining  gold  in  cyanide  solutions  proposed  by  Christy  and 
A.  Whitby.     (See  Part  VIII.) 


SECTION   VII 

TREATMENT   OF   CUPRIFEROUS   ORES 

THE  causes  which  render  the  treatment  of  cupriferous  ores 
by  the  cyanide  process  particularly  difficult  have  already  been 
discussed  in  the  earlier  parts  of  this  book;  they  may  be  sum- 
marized thus:  (1)  From  certain  minerals,  notably  the  carbonates 
and  oxides,  copper  is  readily  dissolved,  forming  a  double  cyanide 
with  the  alkaline  cyanide.  (2)  The  metal  coats  the  zinc  shavings 
in  the  boxes  with  a  thin  adherent  metallic  film,  which  prevents 
the  deposition  of  gold  and  silver.  (3)  The  presence  of  much 
copper  in  the  precipitate  gives  rise  to  a  low-grade  bullion,  as  the 
metal  is  only  imperfectly  removed  in  the  ordinary  smelting  and 
refining  operations: 

The  remedies  which  have  been  applied  or  proposed  are,  for 
the  most  part,  as  follows:  (1)  The  copper  is  removed  from  the 
ore  by  a  preliminary  operation,  previous  to  cyanide  treatment. 

(2)  The  double  cyanide  is  decomposed  in  such  a  manner  that 
the  copper  is  separated  and  the  free  alkaline  cyanide  regenerated. 

(3)  A  modification  of  the  precipitation  process  is  used,  whereby 
the  gold,  silver,  and  copper  may  be  precipitated  simultaneously 
or  successively.     (4)  The   precipitate   or  the   bullion   undergoes 
special  refining  processes  for  separation  of  the  copper  and  other 
base  metals. 

PRELIMINARY  TREATMENT  FOR  REMOVAL  OP  COPPER 

Sulphuric  Acid.  —  In  cases  where  the  copper  exists  as  car- 
bonate, satisfactory  extractions  have  sometimess  been  obtained 
by  giving  a  preliminary  wash  with  dilute  sulphuric  acid.  This 
system  was  at  one  time  applied  at  the  Butters  Plant,  Virginia 
City,  and  has  been  used  at  Cobar,  New  South  Wales,  by  Messrs. 
Nicholas  and  Nicols.1  The  solution  used  at  the  latter  plant 
averaged  0.65  per  cent.  H2SO4.  The  liquor  drawn  off  was  passed 

iW.  S.  Brown,  "Trans.  I.  M.  and  M.,"  XV,  445. 
310 


TREATMENT   OF   CUPRIFEROUS   ORES  311 

through  boxes  containing  scrap-iron  for  precipitation  and  recovery 
of  the  copper.  The  charges  in  the  vats  were  then  water-washed, 
mixed  with  a  sufficient  quantity  of  lime  to  neutralize  any  remain- 
ing acidity,  and  transferred  to  other  vats,  where  they  were  treated 
with  cyanide,  up  to  0.3  per  cent.  KCy,  for  extraction  of  the  gold. 
The  first  cyanide  solution  used  ran  off  with  little  or  no  cyanide 
and  generally  with  low  gold  values;  this  was  precipitated  in  a 
special  zinc-box  and  again  used  for  the  final  wash  before  dis- 
charging. Some  interesting  features  in  connection  with  this  plant 
were  the  use  of  charcoal  after  the  zinc-box  for  the  recovery  of 
gold  not  precipitated  by  zinc  from  weak  solutions,  and  the  use 
of  nitric  acid  in  the  clean-up.  The  acid  vats  had  a  capacity  of 
25  tons  and  the  cyanide  vats  of  75  tons,  so  that  three  charges 
of  the  acid  vats  were  treated  together  in  each  cyanide  vat.  The 
acid  treatment  consisted  of  10  to  12  tons  of  dilute  sulphuric  acid 
(0.65  per  cent.),  followed  by  two  water-washes.  The  acid  was 
first  partially  drained  off,  then  allowed  to  digest  in  contact  with 
the  ore  for  an  hour  or  so,  and  finally  passed  slowly  through  the 
scrap-iron  boxes.  In  the  cyanide  treatment,  15  tons  of  weak 
solution  were  used  to  displace  moisture;  this  solution  carried  little 
gold,  and  was  used  again  as  a  final  wash  before  discharging;  after 
passing  slowly  through  a  zinc-box  it  was  allowed  to  flow  through 
about  20  cu.  ft.  of  packed  charcoal.  The  precipitate  from  the 
zinc-boxes,  in  which  much  lead  acetate  was  used,  was  extremely 
base,  and  was  first  treated  with  sulphuric  acid  for  removal  of 
the  zinc,  then  washed  with  distilled  water,  and  finally  treated 
with  nitric  acid  to  dissolve  copper  and  lead.  In  order  to  ,prevent 
gold  going  into  solution,  any  chlorides  present  were  precipitated 
with  silver.  Bullion  was  produced  over  900  fine. 

Sulphurous  acid  has  been  tried  as  a  preliminary  solvent  of 
copper  by  A.  von  Gernet  and  others,  and  is  claimed  to  have  some 
action  not  only  on  carbonates,  but  also  on  sulphides  of  copper. 

Ammonia.  —  The 'use  of  ammonia  as  a  preliminary  solvent  of 
copper  has  been  suggested  by  H.  Hirsching.1  The  ammoniacal 
solution  is  distilled,  and  the  ammonia  recovered  for  re-use,  while 
the  copper  is  precipitated  as  oxide. 

Double  Cyanides  of  Copper. — It  has  been  shown  by  Scrymgeour2 
that  cupriferous  cyanide  solutions  are  capable  of  extracting  a 

1  H.  Hirsching,  "  The  Ammonia  Process." 
2"  E.  and  M.  J.,"  Dec.  20,  1902,  p.  816. 


312  THE  CYANIDE  HANDBOOK 

further  quantity  of  copper  from  certain  ores.  The  copper  is 
finally  recovered  from  this  solution  by  electrolysis,  with  regenera- 
tion of  a  part  of  the  cyanides.  After  this  preliminary  wash,  the 
ore  is  cyanided  as  usual  and  the  solutions  precipitated  electrically. 
This  process  appears  to  depend  on  the  instability  of  the  cupri- 
cyanides  of  the  alkalis,  which  are  readily  transformed  into  cupro- 
cyanides  by  taking  up  a  further  quantity  of  copper. 

PRECIPITATION  OF  COPPER  FROM  CYANIDE  SOLUTIONS 

Several  methods  have  been  suggested  for  precipitating  copper 
from  cyanide  solutions.  We  have  already  described  the  elec- 
trolytic method  practised  at  Butters'  Salvador  mines  (see  Section 
V,  above),  and  the  effect  of  copper  in  the  zinc-boxes,  with  and 
without  the  lead-zinc  couple,  has  been  discussed.  It  is  well  known 
that  certain  acids  precipitate  copper  from  cyanide  solutions  as 
white  insoluble  cuprous  cyanide.  It  has  been  proposed  by  H.  A. 
Barker  *  to  use  sulphuric  acid  for  precipitating  copper  and  gold 
from  the  solutions,  which  are  then  to  be  filtered  and  made  alkaline 
with  caustic  soda;  it  is  stated  that  cyanide  is  regenerated  in  the 
process,  but  the  portion  of  cyanogen  precipitated  with  the  copper 
is  obviously  lost.  The  reactions  are  probably  as  follows: 

K2Cu.Cy4  +  H2SO4  =  Cu,Cy2  +  2HCy  +  K2SO4 
HCy  +  NaOH  =  NaCy  +  H2O. 

It  is  also  suggested  that  this  method  of  precipitation  might  be 
used  as  an  adjunct  to  Scrymgeour's  process,  described  above, 
the  weak  solution  used  as  a  preliminary  wash  in  that  process  being 
precipitated  with  sulphuric  acid  when  sufficiently  charged  with 
copper. 

USE  OF  AMMONIA  AS  AUXILIARY  SOLVENT 

It  has  been  found  that  a  mixture  of  ammonia  or  ammonium 
salt  with  cyanide  forms  a  much  more  effective  solvent  for  gold 
in  cupriferous  ores  than  cyanide  alone.  When  an  ammonium 
salt  is  mixed  with  an  equivalent  of  an  alkaline  cyanide  in  solution, 
decomposition  takes  place,  with  formation  of  ammonium  cyanide, 
thus: 

2KCN  +  (NHOiSCX  =  K£S04  +  2NH4CN. 


"Trans.  Inst.  Min.  and  Met."  XII,  p.  399  (May  21,  1903). 


TREATMENT  OF  CUPRIFEROUS   ORES  313 

A  series  of  experiments  made  by  Jarman  and  Brereton  * 
appears  to  show  that  a  mixture  of  ammonia  and  potassium  cy- 
anide dissolves  less  copper  than  does  potassium  cyanide  alone. 
A  process  based  on  the  use  of  this  solvent  has  been  applied  by 
Bertram  Hunt  in  treating  tailings  from  the  Comstock  Lode,  and 
cupriferous  ore  at  Dale,  California.  The  observations  on  which 
this  method  is  based  are  summarized  as  follows  by  J.  S.  MacArthur, 
in  a  discussion  on  Jarman  and  Brereton's  results:2  (1)  A  weak 
solution  of  ammonia  generally  does  more  work  as  a  solvent  of 
copper  than  a  corresponding  quantity  of  a  stronger  solution. 
(2)  A  solution  of  ammonia  along  with  a  cyanide  dissolves  less 
copper  than  the  sum  of  the  amounts  dissolved  by  the  solvents 
separately.  (3)  For  ordinary  strengths  of  cyanide  and  ordinary 
grades  of  ore,  the  addition  of  ammonia  equal  to  0.11  per  cent,  of 
NH3  produces  a  solution  having  a  maximum  solvent  effect  on 
gold  and  a  minimum  solvent  effect  on  copper. 

»"  Trans.  Inst.  Min.  and  Met."  XIV,  p.  289  (Feb.  16,  1905). 
it.,  p.  331. 


PART  VII 
ASSAYING 


SECTION  I 
SAMPLING 

(A)  SAMPLING  OF  ORES  AND  SIMILAR  MATERIAL  IN  BULK 

Samples  of  Hard,  Coarse  Material.  —  The  sampling  of  ore  "  in 
place"  does  not  generally  come  within  the  limits  of  the  work 
carried  out  by  the  staff  of  a  cyanide  plant.  It  may  be  necessary, 
however,  in  certain  cases,  to  deal  with  large  masses  of  coarsely 
broken  rock,  such  as  ore  dumps,  ore  as  delivered  from  the  mine 
to  the  mill,  slag  heaps,  and  other  similar  accumulations  of  hard 
material,  so  that  a  few  words  on  the  methods  of  sampling  them 
may  not  be  out  of  place. 

Definition  of  Sample.  —  The  essential  point  in  all  sampling 
is  to  select  from  a  relatively  large  mass  of  material,  containing 
various  ingredients  unevenly  distributed,  a  relatively  small 
quantity  which  shall  contain  each  of  these  ingredients  in  the  same 
proportions  as  those  which  occur  in  the  entire  mass. 

Sampling  Large  Ore  Heaps.  —  A  large  pile  of  ore  is  generally 
sampled  in  the  first  instance  by  making  cuts  into  it  at  various 
points  round  the  base;  when  circumstances  allow,  a  channel  is 
dug  right  across  the  heap  through  the  center,  or,  better,  two 
or  more  intersecting  channels.  A  plan  sometimes  adopted  is  to 
shovel  alternately  to  right  and  left,  and  to  throw  every  third 
shovelful  into  a  barrow,  the  portion  going  into  the  barrow  con- 
stituting the  sample.  The  assumptions  involved  in  this  process 
are:  (1)  That  a  cut  made  through  the  heap  from  side  to  side, 
passing  through  the  center,  will  consist  of  material  of  the  same 
average  composition  as  the  entire  heap;  and  (2)  that  every  third 
shovelful  is,  on  the  average,  of  the  same  composition  as  the  re- 
maining two.  The  first  of  these  assumptions  appears  less  justifi- 
able than  the  second;  hence  it  is  safer  to  make  more  than  one 
channel. 

Coning  and  Quartering.  —  The  further  division  of  the  sample 
must  generally  be  preceded  by  breaking  up  the  larger  lumps, 
which  may  be  done  either  mechanically  or  by  hand.  For  this 

317 


FIG.  41.  — Vezin  Sampler,  as  furnished  by  Hadfield's  Steel  Foundry  Co. 

Sheffield. 


SAMPLING 


319 


purpose  it  may  be  spread  evenly  over  a  smooth  surface,  such  as  a 
cement  floor,  and  any  pieces  broken  up  that  are  obviously  larger 
than  the  rest.  The  entire  sample  is  then  mixed  by  turning  over 
with  a  shovel;  to  ensure  thorough  mixing  the  process  of  "coning" 
is  often  resorted  to.  A  space  is  swept  clean,  and  the  ore  thrown 
into  this,  a  shovelful  at  a  time,  each  shovelful  being  thrown  on 
the  top  of  the  conical  heap  so  formed,  so  that  the  material  rolls 
down  as  evenly  as  possible  on  all  sides.  If  the  heap  is  still  very 
large,  it  may  be  again  sampled  by  trenching;  if  not  too  large  to 
be  conveniently  handled,  it  is  spread  out  in  a  circular  flat-topped 
heap  and  "  quartered  "  by  means  of  boards  held  edgewise  across 
the  center  so  as  to  divide  it  into  four  segments  as  nearly  equal  as 
possible.  Another  method  is  to  form  the  material  into  a  ring  on 
the  floor,  and  make  a  heap  by  shoveling  toward  the  center. 

The  operations  of  coning  and  quartering  are  repeated  succes- 
sively a  number  of  times;  each  time  two  opposite  quarters  are 
rejected  and  removed  from  the  floor,  and  the  remainder  broken 
smaller  before  proceeding  to  quarter  again.  Care  must  be  taken 
to  sweep  away  all  dust  belonging  to  the  rejected  portions  before 
mixing  the  other  quarters. 

Sizes  to  which  Samples  must  be  Crushed.  —  The  degree  of  crush- 
ing necessary  at  each  stage  will  depend  on  the  nature  of  the 
material,  and  must  be  varied  in  special  cases.  The  following 
figures  are  given  by  A.  Harvey  l  as  representing  the  sizes  found 
to  be  safely  allowable  in  actual  work  with  a  Vezin  automatic 
sampling  machine,  cutting  out  J  of  the  entire  mass  put  through 
at  each  operation.  (This  machine  is  so  constructed  that  it  deflects 
the  entire  Stream  falling  through  a  chute  at  regular  intervals  of 
time;  —  say  every  two  or  three  seconds.)  (See  Fig.  41.) 

TABLE  I.  —  ALLOWABLE  SIZES  OF  ORE  PIECES  IN  SAMPLING 


Diameter  of  Largest 
Pieces  in  Sample: 
Inches 

Minimum  Weight 
of  Sample: 
Pounds 

Diameter  of  Largest 
Pieces  in  Sample: 
Inches 

Minimum  Weight 
of  Sample: 
Pounds 

5J 

79,300 

f 

256 

4 

69,109 

i 

32 

3i 

44,958 

i 

4 

2i 

16,384 

A 

| 

H 

2,048 

* 

A 

Min.  and  Sci.  Press,"  LXXXVIII,  p.  78  (Jan.  30,  1904). 


320  THE  CYANIDE  HANDBOOK 

W.  Glenn  *  gives  the  following  rules,  applicable  to  such  ma- 
terial as  10  per  cent,  copper  ore,  originally  in  a  10-ton  pile  con- 
sisting of  large  lumps;  1  ton,  obtained  as  a  sample  by  "trenching" 
as  above  described,  is  quartered  to  500  lb.,  breaking  the  larger 
lumps  with  a  hammer.  This  is  treated  as  follows: 

Diameter  of  Weight  o' 

largest  pieces:  sample: 

Inches  Pounds 

1     500 

£     250 

"fine  gravel"   125 

"coarse  sand" 60 

Proceed  to  mix  and  quarter  on  a  sheet  of  paper. 

"At  this  point  the  sample  would  weigh  about  15  lb.;  its  larger 
grains  would  be  in  size  like  coarse  sand.  It  would  be  safe  now, 
without  further  breaking,  to  mix  and  quarter  it  twice,  or  until  its 
weight  did  not  exceed  4  lb.  Run  this  through  the  mortar  and 
then  mix  and  quarter  it  twice,  or  down  to  1  lb.  weight.  Grind 
this  to  something  approaching  powder,  and  for  the  last  time  mix 
and  quarter  it." 

Relation  of  Size  of  Sample  to  Grade  of  Ore.  —  D.  W.  Brunton  2 
discusses  the  whole  subject  of  mixing  and  quartering  from  a 
mathematical  standpoint,  and  shows  that  the  size  to  which  ore 
must  be  crushed,  so  that  the  error  in  sampling  may  be  within 
allowable  limits,  depends:  (1)  On  the  weight  or  bulk  of  sample 
(the  smaller  the  sample  the  finer  it  must  be  crushed) ;  (2)  on  the 
relative  proportion  between  the  value  of  the  richest  minerals  and 
the  average  value  of  the  ore  (with  high-grade  ores  we  may  crush 
more  coarsely  than  with  low-grade,  for  the  same  percentage  of 
error);  (3)  on  the  specific  gravity  of  the  richest  mineral  present. 
The.  higher  the  specific  gravity  of  the  richest  mineral,  the  greater 
the  value  of  a  particle  of  given  size  and  grade,  and  hence  the 
greater  the  influence  of  such  particle  on  the  sample.  Finer  crush- 
ing is  therefore  required  when  the  rich  material  is  also  of  high 
specific  gravity. 

Formula  for  Dividing  Samples.  —  S.  A.  Reed  3  gives  the  fol- 
lowing formula  for  determining  the  maximum  diameter  allowable 
for  the  particles  in  any  stage  of  the  sampling  of  a  given  ore: 

i  Trans.  A.  I.  M.  E.,  XX,  p.  155  (June,  1891). 

a  Trans.  A.  I.  M.  E.,  XXV,  p.  826  (October,  1895). 

3"  Sch.  Mines  Quart.,"  VI,  p.  351  (1885). 


SAMPLING 


321 


D  •-=  diameter  of  largest  pieces  in  inches; 

p  =  quantity  of  the  lot  in  Troy  ounces; 

/  =  number  of  parts  into  which  p  is  to  be   divided    (one   part   to   be 

chosen  as  sample) ; 
k  =  percentage  of  metal  sought  (gold  or  silver)  in  the  richest  specimens 

of  the  lot: 

s  =  sp.  gr.  of  richest  minerals; 
m  =  average  grade  of  ore  (ounces  per  ton); 
a  —  number  of  pieces  of  D  size  and  k  value  that  can  be  in  excess  or 

deficit  in  the  portion  chosen  as  sample; 
I  =  largest  allowable  percentage  of  error. 

Before  cutting  to  -,  we  must  crush  or  grind  the  lot  so  that 


D  =  .053 


m  p  I 


k  (f  -  1)  a 

The  following  table  is  given  for  ores  of  different  grades,  assum- 
ing in  all  cases  that  s  =  7,  I  =  1,  and  that  with  samples: 


Class 

A, 

m 

=    50 

k 

= 

1 

Medium, 

tt 

B, 

m 

=    75 

k 

= 

10 

high-grade, 

n 

c, 

m 

=  500 

k 

= 

30 

very  rich. 

TABLE 

II 

VALUE  OF  D,  IN  INCHES 


aampie  JK.eauceu  irom 

Class  A 

Class  B 

Class  C 

100  to     10  tons        .... 

5.28 

2  96 

2  58 

10  to       1  ton  - 

2  46 

1  38 

i  o 

2000  to  200  Ibs  

1.14 

06 

0  56 

200  to       5    " 

03 

0  18 

01  A 

5  Ibs.  to  10  assay  tons.  .  .  . 

0.034 

0.02 

0.018 

These  figures  correspond  roughly  with  those  given  by  Harvey. 
(See  above.) 

Sampling  Ore  in  Mine.  —  As  the  assayer  may  occasionally 
be  called  upon  to  take  samples  of  ore  from  the  mine  itself,  the 
following  description  of  the  method  employed  on  the  Rand  is 
quoted  from  a  paper  by  G.  A.  Denny  —  "  Observations  on  Sam- 
pling, Computation  of  Assay  Averages,"  etc.1 

"The  sampling  of  the  mine  is  entrusted  to  men  of  experience 
who  take  as  their  equipment  a  water  squirt,  with  which  to  wash 

i  Tr^ns.  A.  I.  M.  E.,  XIX,  p.  294  (June  15,  1900). 


322 


THE  CYANIDE   HANDBOOK 


down  the  rock  at  the  point  to  be  sampled,  hammer,  chisels  (both 
diamond  and  chisel-pointed),  a  receptacle  in  which  to  catch  the 
samplings,  and  sacks  about  15  in.  deep  and  9  in.  wide  wherein 
to  place  the  completed  sample.  .  .  .  The  sampler  first  proceeds 
to  measure  equal  distances  along  the  level,  rise,  or  other  work- 
ing which  he  is  to  sample.  The -distances  taken  are  either  5-ft. 
or  10-ft.  intervals;  in  the  case  of  thin  rich  leaders,  always  5  ft. 
Having  chalked  or  otherwise  marked  the  intervals,  he  proceeds 
to  the  work  of  sampling.  In  cases  where  the  reef  is  thin,  say 
from  1  in.  to  3  in.  in  width,  the  sample  is  taken  over  a  width  of 
6  in.,  that  width  being  carefully  channeled  out  to  a  certain  breadth 
and  depth,  so  that  as  nearly  as  possible  a  true  average  may  be 
obtained.  Samples  should  be  taken  of  approximately  a  minimum 
weight  of  5  to  6  lb.;  in  general  the  bigger  the  sample  the  nearer 
it  is  to  the  true  average." 

When  the  reef  is  "solid"  (i.e.,  contains  no  waste),  and  less 
than  18  in.  wide,  it  is  sampled  as  one  section;  if  of  more  than  18  in. 
width,  it  is  sampled  in  so  many  sections  of  18  in.,  each  section 
being  separately  sacked  and  recorded.  This  is  done  to  avoid 
getting  undue  quantities  of  ore  from  one  section,  as  may  happen 
when  the  hanging  and  foot-wall  sides  are  of  different  character. 
"  In  cases  where  the  reef  is  divided  into  bands  of  ore  and  quartzite, 
only  the  ore  is  sampled,  the  bands  of  waste  being  measured  and 
calculated  on  the  total  sampled  width  in  the  following  manner": 

TABLE  III 


Band 

Width  in  Inches 

Nature 

Assay  Value:    Dwts. 

Assay  —  Inches 

A  

6 

Reef 

15 

90 

B  

c 

12 
10 

Waste 
Reef 

20 

200 

D  
E    

30 
2 

Waste 
Reef 

60 

120 

60 

6.83 

410 

Where  samples  have  been  taken  at  regular  intervals,  the  aver- 
age assay  is  found  by  dividing  the  total  assay-inches  by  the  sum 
of  the  widths  in  inches  of  all  the  samples  taken. 

Where  samples  have  been  taken  at  irregular  intervals,  the 
length  of  reef  represented  by  each  sample  also  enters  into  the 
calculation. 


SAMPLING  323 

It  may  be  added  that  all  mine  samples  should  be  taken  as 
nearly  as  possible  in  a  plane  at  right  angles  both  to  the  dip  and 
strike  of  the  vein  or  deposit  to  be  sampled;  otherwise  an  erroneous 
impression  will  be  given  of  the  quantity  of  ore  represented. 

Machinery  for  Crushing  Samples.  —  The  work  of  breaking  up 
the  larger  lumps,  before  mixing  and  dividing  ore  samples,  is  carried 
out  either  by  hand,  with  a  large  hammer  and  anvil,  or  by  machines, 
of  which  the  two  principal  types  are  represented  by  the  Blake 
and  Gates  crushers  respectively.  The  finer  crushing  is  performed 
by  smaller  machines  of  the  same  types,  or  by  the  pestle  and 
mortar,  or  by  machines  imitating  the  action  of  the  latter.  Crushers 
of  the  Ball  mill  type  are  unsuitable  for  sampling  work  on  account 
of  the  labor  and  difficulty  of  cleaning  them  effectively.  The 
finest  crushing  is  best  done  on  a  flat  steel  or  cast-iron  plate 
with  raised  edges  on  three  sides  (known  as  a  "buckboard"), 
the  ore  being  ground  on  this  by  means  of  a  heavy  iron  block 
("muller"),  worked  backwards  and  forwards  by  means  of  a 
wooden  handle. 

Precautions  in  Preparing  Samples.  —  Attention  may  here  be 
drawn  to  certain  points  of  the  utmost  importance,  neglect  of 
which  is  probably  the  chief  calise  of  inaccuracy  in  the  preparation 
of  ore  samples  for  assay: 

(a)  When  any  portion  has  been  selected  as  a  sample  and  is 
to  be  passed  through  a  sieve  of  particular  mesh,  the  entire  por- 
tion so  selected  must  be  made  to  pass  the  sieve.  If  the  harder 
portions,  which  naturally  resist  crushing  the  longest,  be  rejected, 
the  sample  is  worthless. 

(6)  After  the  operations  of  crushing,  sifting,  etc.,  have  been 
completed  on  one  sample,  every  appliance  used  in  the  process 
should  be  carefully  cleaned  before  proceeding  with  another 
sample. 

(c)  After  crushing  and  sifting,  and  before  dividing,  every 
sample  must  be  thoroughly  mixed.  The  operation  of  sifting  in 
itself  causes  a  certain  amount  of  separation  in  the  different  in- 
gredients, so  that  the  sifted  sample  is  never  homogeneous. 

When,  as  is  frequently  the  case  in  mine  or  cyanide  works' 
assay  offices,  the  preparation  of  the  sample  is  entrusted  to  natives 
not  under  close  supervision,  one  or  all  of  these  precautions  will 
probably  be  shirked. 

Cleaning  Sampling  Implements.  —  Great  care  is  necessary  in 


324  THE  CYANIDE   HANDBOOK 

order  to  prevent  the  mixing  of  one  sample  with  material  from 
others,  or  with  foreign  impurities.  All  vessels  and  instruments 
used  should  be  so  constructed  that  they  may  be  easily  cleaned. 
The  absence  of  this  condition  is  a  fatal  drawback  to  various  other- 
wise effective  devices  which  have  been  designed  for  mechanically 
crushing,  mixing,  and  dividing  samples. 

Sieves  for  Samples.  —  The  sieves  can  generally  be  cleaned 
effectively  with  a  hard  brush;  but  sometimes  it  may  be  necessary 
to  pass  through  the  crushers,  sieves,  etc.,  a  quantity  of  barren 
rock,  sand,  charcoal,  or  other  material  for  the  purpose  of  remov- 
ing adhering  particles  of  a  previous  sample.  The  sieves  used  for 
this  purpose  are  of  brass-wire  screening,  set  in  a  metal  frame; 
as  an  additional  precaution  they  may  be  soldered  all  round  on 
both  sides  at  the  joint  of  the  screen  with  the  frame.  All  sheets 
of  iron,  cloth,  and  rubber,  and  all  sampling  floors  and  tables, 
should  be  carefully  swept  and  dusted  after  each  sample  is  finished; 
they  should  also  be  washed  occasionally. 

Necessity  for  Separate  Sampling  Room.  —  Whenever  possible, 
the  room  in  which  the  samples  are  crushed  and  sifted  should  be 
entirely  distinct  from  the  assay  room.  These  preliminary  opera- 
tions inevitably  cause  a  certain  amount  of  dust  which  should  be 
carefully  kept  away  from  the  supplies  of  flux,  and  from  the  cruci- 
bles and  other  utensils  used  in  the  assay  itself. 

Importance  of  Sampling.  —  The  importance  of  correct  sampling 
can  hardly  be  overestimated;  it  is  obvious  that  the  subsequent 
assay  is  valueless,  however  carefully  conducted,  unless  the  sample 
assayed  really  represents  the  average  composition  of  the  material 
to  be  examined. 

(B)  SAMPLING  OF  SAND  AND  SIMILAR  MATERIAL 

In  cyanide  plants  we  have  to  deal,  as  a  rule,  with  material 
which  has  already  been  more  or  less  finely  crushed,  and  in  most 
cases  with  ore  from  which  the  coarser  metallic  particles  have 
already  been  removed  by  amalgamation. 

Difficulties  of  Sand  Sampling.  —  To  obtain  a  correct  average 
sample,  representing,  say,  the  material  delivered  from  the  mill 
to  the  cyanide  tanks  during  a  run  of  24  hours,  or  the  charge  run 
into  some  particular  tank,  is  by  no  means  so  simple  a  matter  as 
might  appear  at  first  sight.  The  crushed  ore  is  usually  far  from 
uniform  in  composition,  and  the  methods  adopted  for  filling  the 


SAMPLING  325 

tanks  tend  to  produce  layers  or  rings  of  material  differing  in  com- 
position and  value  from  the  remainder. 

Points  where  Samples  may  be  Taken.  —  Samples  for  regulating 
the  work  in  a  sands  plant  may  be  taken:  (1)  Before  entering  the 
tanks;  (2)  in  place,  after  the  tanks  are  filled;  (3)  while  the  tanks 
are  being  discharged.  Where  the  sand  is  collected  in  one  tank 
and  treated  in  another,  the  sampling  is  often  done  during  the 
transfer  from  the  collecting  to  the  treatment  tank. 

Samples  Taken  before  Charging  Tanks.  —  It  is  customary  in 
many  reduction  works  to  take  two  samples  daily  in  the  battery, 
one  representing  the  material  passing  through  the  screens  of  the 
mortar-boxes  immediately  before  it  comes  in  contact  with  the 
amalgamated  plates,  and  the  other  after  it  leaves  the  plates  and 
enters  the  launder  leading  to  the  hydraulic  separators.  These 
samples  are  taken  by  placing  a  metal  scoop  or  other  suitable 
vessel  across  the  whole  width  of  the  discharge,  and  intercepting 
a  portion  of  it  at  regular  intervals  (say  every  hour).  The  por- 
tions so  collected  are  transferred  to  a  bucket,  and  at  the  end  of 
the  day's  run  the  combined  sample  is  drained,  mixed,  quartered 
down,  and  assayed. 

Automatic  Samplers.  —  An  automatic  sampler  is  sometimes 
used  on  the  launder  leading  to  the  separators.  These  samplers 
are  of  various  designs,  the  general  principle  being,  however,  that 
the  entire  stream  of  pulp  is  diverted  into  a  special  vessel  for  a 
few  seconds  at  regular  intervals  of  time.  D.  Simpson1  states  that 
at  the  New  Goch  G.  M.  Company,  the  method  of  catching  the 
outflow  from  the  delivery  hose  at  regular  intervals,  and  also  that 
of  the  automatic  sampler,  were  discarded  at  an  early  date  as  unre- 
liable. In  general,  it  may  be  remarked  that  when  intercepting 
a  stream  by  means  of  a  scoop  it  is  extremely  difficult  to  avoid 
loss  by  splashing,  so  that  the  sample  taken  in  this  way  is  liable 
to  contain  an  undue  proportion  of  the  coarser  and  heavier  par- 
ticles. 

Truck  Samples.  —  In  cases  where  comparatively  dry  sands, 
such  as  accumulated  tailings,  are  to  be  treated,  and  these  are  de- 
livered into  the  tanks  in  trucks  (cars),  it  is  usually  found  that  a 
satisfactory  sample  of  the  charge  can  be  obtained  by  taking  small 
equal  portions  from  each  truckload,  provided  the  number  of 
loads  required  to  fill  the  tank  is  fairly  large. 

i "  Sand  Sampling  in  Cyanide  Works,"  I.  M.  M.,  Bull.  No.  25,  Oct.  11,  1906,  p.  6. 


326  THE  CYANIDE   HANDBOOK 

Sand  Samples  taken  in  Place  by  Sampling-Rod.  —  After  the 
tanks  have  been  filled  it  is  customary  to  take  a  sample  of  the  con- 
tents by  means  of  a  sampling-rod.  This  consists  of  a  metal  tube, 
long  enough  to  penetrate  the  whole  vertical  depth  of  the  material 
to  be  sampled  —  say  from  4  to  10  ft.  length  and  1J  to  2  in. 
diameter.  This  tube  is  slit  from  the  bottom  to  within  a  few  inches 
of  the  upper  end  and  is  provided  with  a  crosspiece  at  right  angles, 
serving  as  a  handle.  The  edges  of  the  groove  and  the  lower  end 
of  the  instrument  are  sharpened  to  allow  it  to  cut  into  the  mass 
of  sand. 

When  the  rod  is  pushed  into  the  charge  with  a  slight  twisting 
motion,  the  hollow  fills  with  sand.  The  rod  is  then  withdrawn 
and  the  surface  scraped  smooth.  The  core  of  sand  is  then  cut 
out  and  set  aside  to  form  part  of  the  sample,  using  a  suitably 
shaped  piece  of  hard  wood  or  metal  for  cleaning  the  groove.  A 
number  of  cores  are  taken  in  this  way  from  various  parts  of  the 
tank,  and  the  whole  mixed  and  quartered.  The  same  instru- 
ment is  commonly  used  for  sampling  tailings  in  dumps  or  pits, 
or  for  any  similar  accumulations  of  moist  sandy  material. 

Objections  to  Rod-Sampling.  —  It  is  a  frequent  complaint  that 
the  sampling-rod  does  not  really  take  out  equal  quantities  of  sand 
at  different  depths  in  the  tank.  In  passing  through  the  upper 
layers,  the  lower  part  of  the  tube  becomes  choked,  especially  if 
the  material  be  somewhat  slimy,  so  that  the  lower  layers  are  not 
represented  at  all,  although  the  rod  has  been  pushed  to  the  bottom 
of  the  tank.  This  difficulty  may  be  partially  obviated  by  taking 
samples  to  half  the  depth  of  the  tank,  cleaning  the  rod,  and  .then 
pushing  it  down  to  the  bottom  of  the  tank  through  the  hole  already 
made,  the  second  portion  taken  thus  representing  only  the  bottom 
layers.  As  it  frequently  happens  that  the  bottom  layer  (6  in.  or 
12  in.)  is  of  very  different  composition  from  the  remainder,  it 
cannot  be  considered  that  this  method  may  be  safely  relied  on  to 
give  accurate  results,  unless  special  precautions  are  taken. 

Location  of  Samples  in  Tank.  —  The  number  of  rod-samples 
taken  per  charge,  and  the  points  at  which  they  are  taken,  are  also 
matters  of  considerable  importance.  If  the  charge  were  abso- 
lutely uniform,  a  single  sample  taken  at  any  point  would  correctly 
represent  its  average  composition.  This,  however,  is  seldom,  if 
ever,  the  case.  When  the  charge  is  not  uniform,  a  better  result 
will  be  obtained  by  taking  samples  in  such  places  that  each  one 


SAMPLING  327 

represents  an  equal  mass  of  sand,  rather  than  by  haphazard 
sampling  in  any  part  of  the  charge.  The  tanks  used  at  the  present 
day  are  practically  always  cylindrical  in  form,  with  a  flat  bottom 
at  right  angles  to  the  sides.  Hence,  by  describing  on  the  upper 
surface  a  number  of  circles  of  varying  diameters,  the  charge  may 
be  divided  into  any  required  number  of  sections,  each  representing 
an  equal,  mass  of  sand.  Thus,  a  circle  40  feet  in  diameter  may  be 
divided  into  4  equal  areas  by  describing  from  its  center  circles 
having  radii  of  10  ft.,  14.14  ft.,  and  17.32  ft.  The  general  formula 
is  as  follows: 

Let  n  =  number  of  equal  areas  required; 
T\,  r-2,  rs,  =  radii  of  circles  described  from  center  of  upper  surface; 

rn  =  radius  of  the  tank  itself; 
Then  a  =  area  of  each  section. 
Then,  a  =  HT,»  =  ir(r22  -  n2)  =  7r(r32  - r*2)  =  ir(r2«-i  -  r2w). 

Hence,  n  =  \/— ,    r2  =  \/2r,,    r3  =  v/3n,    r»  =  \/n  •  n,    a  =  ir^L. 
ir  n 

These  areas  may  again  be  subdivided  by  diameters  of  the 
40-ft.  circle  inclined  at  equal  angles.  Thus,  by  taking  2  diameters 
at  right  angles  we  obtain  16  equal  areas,  and  by  taking  a  rod- 
sample  as  nearly  as  possible  in  the  center  of  each  we  should  obtain 
a  tolerably  good  average  of  the  whole  charge. 

Causes  of  Irregularity  in  Distribution  of  Sand.  —  From  the 
above  it  will  be  evident  that  the  method  sometimes  adopted  of 
taking  samples  at  equal  distances  along  a  diameter  gives  an 
undue  proportion  of  material  from  the  central  parts  of  the  tank, 
where  the  coarser  and  heavier  particles  generally  tend  to  collect. 
The  lumps  of  slime  generally  accumulate  at  the  bottom  and  sides 
of  the  tank.  When  material  is  transferred  from  an  upper  to  a 
lower  tank,  the  lumps  of  slime  and  any  lighter  or  finer  material 
tend  to  roll  down  the  sides  of  the  cones  formed  below  each  dis- 
charge door,  and  form  layers  and  walls  on  the  filter-mat  at  the 
junctions  of  the  cones  with  one  another  and  the  sides  of  the 
tank. 

Section  Sampling.  —  Where  the  conditions  permit,  according 
to  Simpson,1  an  accurate  sample  may  be  obtained  by  discharging 
sand  from  a  tank,  leaving  a  vertical  face  in  the  plane  of  a  diameter 
of  the  tank.  This  is  divided  into  a  number  of  horizontal  zones 
of  equal  width,  and  samples  taken  by  scraping  the  face  of  each 

d.,  p.  3. 


328  THE  CYANIDE  HANDBOOK 

zone  into  a  separate  bucket.  These  samples  are  then  assayed 
separately,  or  a  combined  sample  is  made  by  mixing  equal  quan- 
tities of  each. 

Samples  taken  while  Discharging  Tanks.  —  When  the  tanks 
are  discharged  by  means  of  trucks,  a  good  sample  of  the  residues 
may  generally  be  obtained  by  taking  with  a  scoop  or,  better, 
with  a  sampling-rod  an  approximately  equal  portion  from  each 
truckload,  the  sample  thus  obtained  being  afterward  mixed  and 
divided.  In  cases  where  the  material  is  entirely  composed  of 
comparatively  small  grains  and  is  fairly  uniform,  only  a  small 
quantity  need  be  taken  from  each  truck.  Where  the  material 
contains  large  lumps,  as  may  be  the  case  with  slimy  tailings,  it 
is  necessary  to  take  larger  amounts.  All  such  lumps  included  in 
the  sample  must  be  thoroughly  broken  up  before  quartering. 

When  the  tanks  are  discharged  by  a  belt-conveyor,  or  similar 
mechanical  device,  samples  may  be  taken,  at  equal  intervals  of 
time,  as  the  material  passes  a  certain  point;  or  an  equal  portion 
may  be  taken  once  or  twice  during  each  revolution  of  the  belt. 

Precautions  as  to  Residue  Samples.  —  When  residue  samples 
have  been  taken  after  cyanide  treatment,  it  is  essential  to  place 
them  in  a  vessel  which  will  not  absorb  liquid,  and  which  is  not 
affected  by  cyanide  in  any  way.  An  ordinary  metal  bucket  is  not 
suitable  for  this  purpose,  but  an  enameled  iron  bucket  in  good 
condition  may  generally  be  used.  The  samples  should  be  kept 
covered  as  much  as  possible,  especially  if  a  moisture  determination 
is  to  be  made. 

Mixing,  Dividing,  and  Quartering  Samples.  —  For  assay  pur- 
poses, all  samples  taken  as  above  described  require  to  be  reduced 
in  bulk.  The  general  principles  of  this  process  are  the  same  as 
those  underlying  the  reduction  of  ore  samples,  already  discussed, 
the  essential  point  being  that  the  average  composition  of  the 
sample  must  not  be  altered.  In  all  cases  a  thorough  mixing  is 
necessary.  The  sample  is  spread  out  on  a  smooth  surface  of 
suitable  material,  and  sufficiently  large  to  allow  of  the  sample 
being  turned  over  freely  with  a  shovel.  When  the  material  is 
not  very  wet,  a  cement  floor  answers  the  purpose.  All  lumps 
must  be  carefully  broken  up,  and  in  many  cases  it  is  very  desir- 
able to  put  the  whole  sample  through  a  coarse  sieve,  after  which 
it  is  reduced  by  coning  and  quartering.  (See  above.)  It  has 
already  been  remarked  that  any  lumps  of  slimes  and  such-like 


SAMPLING  329 

material  tend  to  roll  to  the  bottom  of  the  cone,  so 'that  it  is  as 
well  not  to  rely  exclusively  on  this  process  for  mixing  the  sample. 
When  the  mixing  is  considered  to  be  sufficient,  the  conical  or 
hemispherical  heap  is  divided  crosswise  into  four  quarters.  Two 
opposite  quarters  are  dug  away  and  rejected.  The  remaining 
quarters  are  mixed  together,  any  lumps  further  broken  up,  and 
again  quartered,  this  operation  being  repeated  until  the  required 
amount  is  obtained  for  the  determinations  needed.  After  the 
weight  of  the  sample  has  been  sufficiently  reduced,  the  mixing 
may  conveniently  be  done  by  rolling  on  a  sheet  of  oil-cloth  or 
rubber,  taking  care  to  alter  the  direction  of  rolling  as  often  as 
possible,  so  as  to  avoid  the  formation  of  bands  of  concentrates. 
In  the  case  of  ordinary  sand  samples  a  very  satisfactory  mixture 
may  be  obtained  by  rolling,  provided  the  surface  be  sufficient  and 
the  operation  be  repeated  several  times. 

Samples  containing  a  moderate  amount  of  moisture  and 
fairly  uniform  in  composition  may  be  divided  by  spreading  out 
in  a  uniform  layer  a  few  inches  thick,  and  selecting  with  a  horn 
scoop,  spatula,  or  other  instrument,  approximately  equal  portions 
at  regular  intervals  all  over  the  layer.  It  is  a  good  plan  to  rule 
two  sets  of  parallel  lines  at  right  angles,  so  as  to  divide  the  layer 
into  a  considerable  number  of  small  equal  squares,  and  to  take 
equal  small  portions  from  each  square.  Before  doing  this,  how- 
ever, the  sample  should  have  been  well  mixed  by  coning,  rolling, 
or  otherwise. 

Moisture  Samples.  —  It  is  frequently  necessary  to  make  a 
determination  of  the  amount  of  moisture  in  charge  or  residue 
samples  in  order  to  calculate  the  dry  weight  of  material  under 
treatment.  Thus,  the  dry  contents  of  a  tank  are  known  if  we 
know  the  average  weight  of  the  truckloads  of  wet  sand  required 
to  fill  it,  the  number  of  such  loads,  and  the  percentage  of  moisture. 
All  such  "moisture  samples"  are  taken  with  as  little  delay  as 
possible.  Probably 'the  most  satisfactory  method  is  to  spread 
out  a  large  quantity  of  the  roughly  mixed  sample,  take  out  por- 
tions at  regular  intervals  in  the  way  described  above,  and  weigh 
on  a  good  balance  500  or  1000  grams  of  the  sample.  This  is 
placed  in  a  porcelain  or  enameled-iron  dish  and  dried  at  the 
same  temperature  that  is  used  for  drying  the  ordinary  assay 
samples.  When  cool,  the  dried  sample  is  again  weighed,  the 
difference  indicating  the  amount  of  moisture.  In  the  case  of 


330  THE  CYANIDE  HANDBOOK 

very  wet  material  (slimes  and  similar  samples)  it  is  best  to  weigh 
dish  and  contents  together,  and'  determine  the  weight  of  the  empty 
dish  after  cleaning  and  drying. 

Drying  Assay  Samples.  —  After  the  sample  has  been  reduced 
by  successive  quarterings  or  otherwise  to  about  5  Ibs.  (or,  say, 
2  kg.),  it  may  conveniently  be  dried  by  heating  in  a  suitable  vessel 
over  a  moderately  hot  fire.  In  this  operation  the  nature  of  the 
material  to  be  treated  must  be  carefully  considered.  Where 
pyrites  is  present,  the  heat  must  not  be  sufficient  to  cause  any 
roasting.  Drying  at  a  temperature  of  100°  or  110°C.  would  in 
general  be  far  too  slow  for  ordinary  assay  work,  though  some  such 
standard  is  usually  adopted  for  samples  required  for  analysis. 
An  effective  arrangement  for  some  time  used  by  the  writer  con- 
sisted of  a  wide  chamber  about  a  foot  high,  with  wooden  and  can- 
vas sides,  the  whole  being  heated  above  and  below  by  means  of 
a  coiled  steam-pipe,  maintaining  a  temperature  of  about  90°  C. 
About  a  dozen  ordinary  samples,  containing,  say,  5  per  cent, 
moisture,  could  be  dried  if  left  over  night  in  this  apparatus. 
Samples  dried  in  this  and  similar  ways  probably  always  retain 
a  small  percentage  of  hygroscopic  moisture;  this,  however,  does 
not  seriously  affect  the  assay,  nor  does  it  affect  the  accuracy  of 
any  calculations  of  the  values  per  ton  of  material,  provided  the 
moisture  sample  has  been  dried  at  the  same  temperature. 

Drying  samples  over  an  open  fire  in  iron  pans,  as  is  frequently 
done,  is  not  to  be  recommended.  Unless  constantly  watched, 
there  is  danger  of  the  sample  being  overheated;  also,  in  removing 
the  sample  from  the  pan,  pieces  of  metal  or  rust  from  the  latter 
are  apt  to  scale  off.  Samples  containing  dissolved  gold  and  silver, 
such  as  the  residues  from  cyanide-treated  tailings,  should  on  no 
account  be  dried  in  unprotected  metal  vessels.  Porcelain  or 
enameled-iron  vessels  are  the  most  suitable,  but  when  these  are 
used  the  temperature  must  be  carefully  regulated. 

Reduction  of  Dried  Sample.  —  When  quite  dry,  the  entire 
sample  must  be  passed  through  a  sieve  of  suitable  mesh,  depend- 
ing on  the  nature  of  the  material.  For  this  first  sifting  a  screen 
of  4  holes  to  the  linear  inch  may  be  used,  to  break  up  any  lumps 
of  slime,  etc.  The  sample  is  then  turned  out  on  an  oilcloth  or 
rubber  sheet,  and  thoroughly  mixed  by  rolling.  All  lumps  not 
passing  the  sieve  are  ground  up  in  a  mortar  or  on  the  buckboard. 
The  softer  lumps  may  be  broken  by  simply  rubbing  on  the  sieve 


SAMPLING  331 

with  a  smooth  block  of  wood  or  cork.  The  use  of  metal  weights 
and  similar  objects  for  this  purpose  is  objectionable,  as  they  tend 
to  wear  the  wires  and  enlarge  the  holes  of  the  sieve. 

It  is  essential  that  the  whole  sample  be  passed  through,  as 
the  portions  remaining  on  the  sieve  are  almost  invariably  of 
different  average  composition  from  the  remainder.  After  sift- 
ing and  mixing,  the  sample  is  quartered,  either  by  hand  or  by 
some  mechanical  device.  Many  different  types  of  apparatus 
have  been  brought  out  for  this  purpose,  mostly  based  on  the 
principle  of  cutting  out  a  given  fraction  (say  J  or  £)  from  a  fall- 
ing stream  of  sand.  The  fraction  retained  as  the  sample  is  then 
passed  through  a  finer  sieve,  all  particles  which  do  not  at  once 
pass  the  sieve  being  crushed  to  the  requisite  degree  of  fineness. 
The  sample  is  then  again  mixed  and  further  divided.  This 
process  is  repeated,  using  successively  finer  sieves,  until  the  assay 
sample  is  obtained.  This  should  be  crushed  at  least  to  60-mesh; 
in  some  cases  it  is  desirable  to  use  a  much  finer  mesh,  say  120  or 
200.  The  finer  crushing  is  generally  done  on  a  buckboard,  as 
described  above. 

Size  of  Grains  at  Different  Stages.  —  The  maximum  size  of 
lumps  allowable  at  any  stage  of  the  process  depends  on  the  weight 
of  the  sample  at  that  stage.  This  subject  is  discussed  above  in 
reference  to  rock  samples,  and  some  examples  are  given  from 
different  writers,  but  no  absolute  rule  can  be  given.  The  point 
should  be  determined,  in  the  case  of  any  particular  class  of  ma- 
terial, by  making  separate  assays  of  each  pair  of  opposite  quarters 
in  one  or  more  lots  of  the  material.  The  following,  frequently 
used  by  the  writer,  may  be  taken  as  an  example  in  dealing  with 
ordinary  sand  charges  and  residues: 

Entire  sample  passed  (wet)  through  J-inch  screen.  From  this 
2000  grams  are  roughly  weighed  out  after  mixing,  dried,  crushed 
to  J  in.,  and  halved. 

1000  grams  crushed  to  10-mesh  and  halved 
500     "  "  30-     "      " 

250     "  "  60-     "      " 

125      "  "  80-     "      for  sample. 

The  last  step  is  taken  only  in  the  case  of  fairly  rich  material. 
The  final  sample  allows  of  4  assays  of  1  assay  ton  each;  or  if  the 
division  is  stopped  at  250  grams  of  4  assays  of  2  assay  tons  each. 


332  THE  CYANIDE  HANDBOOK 

Weight  of  the  Final  Sample.  —  Sufficient  material  should  be 
retained  to  allow  of  the  assay  being  repeated  three  or  four  times 
if  necessary.  Generally  speaking,  the  poorer  the  sample,  the 
larger  must  be  the  quantity  taken  for  each  assay.  The  assay  charge 
commonly  taken  varies  from  30  to  60  grams,  but  in  special  cases 
it  may  be  as  low  as  15  grams  or  as  high  as  250  grams;  the  assay 
sample  may  therefore  vary  from  60  to  1000  grams. 

Sampling  Slimes.  —  L.  Ehrmann  *  gives  the  following  method 
for  sampling  "battery  slimes."  The  slimes  are  put  through  a 
small  filter-press  after  the  pulp  has  been  thoroughly  mixed;  then 
two,  three,  or  more  cakes  are  made,  according  to  the  volume  of 
the  original  sample,  the  cakes  weighing  about  1J  kg.  wet  or  1  kg. 
dry.  Now  from  each  fresh  cake  two  opposite  triangular  parts  are 
cut  and  the  portions  so  selected  are  made  into  a  pulp  with  water 
and  again  put  through  the  press,  until  only  one  cake  is  obtained. 
This  cake  will  be  an  average  of  the  lot,  and  will  weigh,  say,  35 
assay  tons.  From  this,  triangular  opposite  parts  are  cut  so  as  to 
get  16  to  17  assay  tons.  This  may  then  be  dried  for  the  assay 
sample. 

'Samples  Containing  Dissolved  Values.  —  When  samples  con- 
tain soluble  gold  and  silver  it  is  best  to  make  a  thorough  extrac- 
tion of  the  soluble  matter,  and  assay  the  extract  and  the  washed 
residue  separately,  then  calculating  the  results  on  the  weight  of 
the  original  sample.  It  has  been  supposed  that  losses  of  precious 
metal  take  place  in  drying  finely  divided  samples  containing 
cyanide  solution,  but  the  evidence  on  this  point  is  not  very  con- 
clusive.2 

1 "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  p.  697. 
.,  II,  372. 


SECTION  II 
ASSAY  OF  A  TYPICAL  SILICEOUS   ORE 

(A)  CRUCIBLE  FIRE  ASSAY 

Object  of  Assaying.  —  The  process  of  assaying  aims  at  extract- 
ing the  whole  of  the  gold  and  silver  in  a  pure  and  weighable  form 
from  a  weighed  portion  of  the  ore  or  other  material  to  be  assayed, 
which  portion  is  assumed  to  be  of  the  same  average  composition 
as  the  entire  mass  which  it  represents. 

Quantity  of  Ore  to  be  Used  for  Assay.  —  The  amount  to  be 
weighed  out  for  the  fusion  will  be  determined  by  the  probable 
richness  of  the  sample. 

Where  results  have  to  be  reported  in  ounces  or  pennyweights 
per  ton,  it  is  convenient  to  use  what  is  known  as  the  "  assay  ton  " 
system.  An  assay  ton  is  a  weight  so  chosen  that  it  contains  as 
many  milligrams  as  there  are  ounces  (troy)  in  a  ton. 

For  the  ton  of  2000  Ib.  this  weight  is  29J  grams  (29166§  mg.) 

For  the  ton  of  2240  Ib.  the  assay  ton  is  32f  grams  (32666f  mg.). 

If  this  weight  be  taken  for  an  assay,  every  milligram  of  metal 
found  will  represent  1  oz.  (or  20  dwt.)  per  ton  of  the  material 
assayed;  if  2  assay  tons  be  taken  for  an  assay,  every  milligram 
found  will  represent  J  oz.  (or  10  dwt.);  or  every  0.1  mg.  will 
represent  1  dwt.  per  ton  of  the  material  assayed. 

The  abbreviations  "  1  a.  t.,"  "2  a.  t.,"  etc.,  are  commonly  used 
to  represent  "one  assay  ton,"  "two  assay  ton,"  etc.  When  not 
otherwise  stated,  the  "ton"  referred  to  in  this  work  is  the  ton 
of  2000  Ibs. 

Assays  are  often  made,  however,  on  an  even  number  of  grams 
(say  30,  60,  or  100) ;  in  this  case,  if  the  result  is  to  be  reported  on 
the  "  ounce  per  ton  "  or  "  pennyweight  per  ton  "  system,  a  table  for 
converting  the  results  must  be  used. 

Where  the  metric  system  is  used  throughout,  1  mg.  per  kilo- 
gram represents  1  gram  per  ton  of  1000  kilograms.  In  this  case  a 
convenient  quantity  for  assay  is  25  or  50  grams: 

1  mg.  on  25  grams  =  40  grams  per  ton. 
1  mg.  on  50      "       =  20       "        per  ton. 
333 


334  THE  CYANIDE  HANDBOOK 

Fluxes.  —  The  "  crucible "  or  "  fusion "  assay  of  an  ore  is 
carried  out  in  several  stages,  the  first  of  which  consists  in  forming 
an  alloy  of  lead  with  the  precious  metals;  other  substances  are 
added  at  the  same  time  to  form  fusible  compounds  with  the  re- 
maining constituents  of  the  ore,  so  that  every  particle  of  precious 
metal  may  readily  sink  through  the  mass  and  alloy  with  the  lead. 
In  order  to  effectively  secure  every  particle  of  gold  and  silver,  it  is 
found  necessary  to  use  a  mixture  which  will  generate  metallic  lead  in 
a  state  of  very  fine  division ;  for  this  purpose  an  oxide  of  lead  mixed 
with  some  reducing  agent  is  necessary;  when  this  is  sufficiently 
heated,  the  latter  acts  upon  the  oxide,  producing  minute  globules 
of  metallic  lead  in  all  parts  of  the  mass;  these  gradually  sink,  at 
the  same  time  combining  with  and  carrying  down  with  them  any 
particles  of  gold  and  silver  which  they  encounter. 

The  remaining  constituents  of  the  ore  fall  into  one  of  two 
groups,  generally  described  as  "acid"  or  "basic."  In  order  to 
effectively  separate  these  from  the  metallic  particles,  substances 
must  be  added  to  form  a  fusible  compound  with  each  of  these 
classes.  Acid  substances  will  require  a  basic  flux,  and  basic  sub- 
stances an  acid  flux.  We  require,  therefore: 

1.  An  oxide  of  lead  (litharge,  red  lead); 

2.  A  reducing  agent  (charcoal,  flour,  argol) ; 

3.  A  basic  flux  (carbonate  of  soda,  bicarbonate  of  soda,  car- 
bonate of  potash); 

4.  An  acid  flux  (borax,  silica). 

Other  substances,  such  as  niter,  fluor-spar,  sulphur,  metallic 
iron,  etc.,  are  occasionally  added  for  special  purposes  (see  below). 

Proportions  of  Ingredients  in  Flux.  —  The  nature  of  the  flux 
necessary  and  the  proportions  and  total  quantity  of  each  ingredi- 
ent should  be  ascertained  by  experiment  for  each  particular  class 
of  sample  which  has  to  be  dealt  with.  The  information  given  on 
this  subject  in  different  text-books  is  contradictory  and  often 
misleading,  but  by  bearing  in  mind  the  object  of  the  different 
classes  of  fluxing  materials,  the  proper  proportions  may  generally 
be  discovered  after  a  few  trials,  and  where  many  samples  of  similar 
material  have  to  be  assayed,  a  large  stock  of  flux  may  be  pre- 
pared for  use. 

Standard  Flux  for  Siliceous  Ores. — The  following  may  be  taken 
as  applicable  to  a  large  number  of  samples  of  what  may  fairly 


ASSAY  OF  A  TYPICAL  SILICEOUS   ORE  335 

be  called  siliceous  or  quartzose  ores.  They  were  adopted  by  the 
writer  after  an  extensive  series  of  experiments  on  an  ore  consist- 
ing mainly  of  silica,  but  containing  a  fair  amount  of  oxide  of  iron, 
and  smaller  quantities  of  the  silicates  of  aluminium,  magnesium, 
etc.: 

Charge  of  ore                                        1  assay  ton  2  assay  tons 

Carbonate  of  soda 32    grams  57  grams1 

Fused  borax 5         "  8      " 

Litharge 57         "  120     " 

Charcoal 1.1      "  2      " 

Size  of  crucible  required G  H 

Weight  of  lead  produced 25     grams  40  grams 

Quality  of  Fluxes.  —  When  large  quantities  of  flux  are  pre- 
pared, the  ingredients  should  be  carefully  mixed,  all  lumps  broken 
up,  and  the  whole  sifted  through  a  coarse  screen  kept  for  this  special 
purpose.  The  flux  should  be  preserved  in  a  suitable  box  or  tin, 
kept  in  a  dry  place,  and  not  exposed  to  dust  from  ore  samples,  etc. 

The  proportions  of  borax  and  soda  to  be  used  will  vary  con- 
siderably with  the  quality  of  these  reagents,  which  sometimes 
contain  a  considerable  percentage  of  moisture  and  other  ingredi- 
ents. It  is  not  by  any  means  unusual  to  find  commercial  "  dry  " 
borax  with  over  30  per  cent,  of  moisture.  If  used  in  the  flux, 
about  double  the  quantities  given  above  must  be  taken,  but  such 
material  should  be  avoided  as  it  swells  enormously  on  heating, 
and  causes  violent  bubbling  in  the  crucible  during  the  early  stages 
of  the  fusion.  There  seems  to  be  no  object  in  using  bicarbonate 
of  soda  in  place  of  the  carbonate;  the  Na2O  being  the  effective 
constituent,  the  use  of  bicarbonate  merely  implies  loss  of  fuel  and 
time  in  expelling  the  extra  quantity  of  carbonic  acid. 

Proportions  of  Litharge  and  Reducer.  —  The  litharge  and  char- 
coal should  be  so  regulated  that  the  button  of  lead  obtained  at 
the  end  of  the  fusion  is  of  convenient  size  for  cupellation,  and 
may  be  reasonably  supposed  to  have  taken  up  practically  the 
whole  of  the  values  in  the  material  fused.  Some  assayers  insist 
on  reducing  the  whole  of  the  lead  from  the  litharge  used  in  the 
flux;  others  are  equally  emphatic  as  to  the  necessity  of  using  a 
large  excess  of  litharge;  in  the  writer's  experience  it  is  best  to 
leave  a  small  excess  of  litharge  in  the  slag.  The  weight  of  lead 
button  found  to  be  most  generally  suitable  is  about  18  to  23  grams 
for  an  assay  on  1  assay  ton  of  ore,  and  25  to  30  grams  for  2  assay 
tons  of  ore. 


336  THE  CYANIDE  HANDBOOK 

In  some  cases,  better  results  are  obtained  by  increasing  both 
litharge  and  reducing  agent  so  as  to  bring  down  a  large  button  of 
lead,  which  is  afterwards  reduced,  as  described  below,  to  a  con- 
venient size  for  cupellation. 

The  special  modifications  of  the  process  for  different  classes 
of  ores  containing  base  metals,  etc.,  will  be  discussed  in  a  later 
section. 

Crucibles.  —  The  crucibles  generally  used  are  fire-clay  pots 
of  different  shapes  and  sizes.  The  kinds  marked  "G"  and  "H" 
are  those  most  generally  useful  for  assays  on  1  assay  ton  and  2 
assay  tons  respectively.  Previous  to  use,  they  should  be  stored 
in  a  warm  dry  place  and  carefully  cleaned  before  charging.  Covers 
of  the  same  material  are  used,  which  serve  to  prevent  the  entrance 
of  coal  or  other  foreign  matter  into  the  crucible  during  the  fusion. 
The  same  crucible  may,  with  care,  be  used  for  five  or  six  succes- 
sive fusions,  but  must  be  carefully  examined  for  cracks  before 
recharging. 

Weighing  the  Assay  Charges.  —  It  is  advisable  to  have  the 
portions  of  flux  needed  for  each  assay  ready  before  weighing  out 
the  ore  charges.  The  flux  need  not  be  weighed  with  great  accu- 
racy; in  fact,  for  all  practical  purposes  the  necessary  amount  may 
be  measured  out  by  means  of  a  small  metal  cup  or  other  con- 
venient instrument  which  allows  of  approximately  equal  quanti- 
ties being  selected. 

The  ore  is  best  spread  out  on  a  sheet  of  smooth  rubber  in  front 
of  the  pulp  balance  or  ore  balance  used  for  weighing.  It  is  as- 
sumed that  the  sample  has  already  been  thoroughly  mixed,  but 
as  an  additional  precaution  the  assay  charge  may  be  chosen  by 
removing  small  amounts  with  a  spatula  at  regular  intervals  all 
over  the  layer  of  ore.  The  charge  is  placed  on  the  left-hand  pan 
of  the  balance  and  the  assay-ton  weight,  or  other  weight  required, 
on  the  right.  The  weight  for  assay  may  then  be  adjusted  by 
adding  or  taking  off  small  portions  of  ore  until  it  is  correct  to 
about  0.1  gram.  In  an  ordinary  assay  it  is  a  waste  of  time  to 
adjust  more  closely  than  this,  as  it  is  obvious  that  a  difference 
of  0.1  gram  on  a  charge  of,  say,  30  grams  would  introduce  an  error 
of  only  y1^  dwt.  in  an  assay  of  a  20-dwt.  ore;  whereas  a  balance 
sensitive  to  T^  mg.  can  only  detect  a  difference  equivalent  to 
oz.,  or  $  dwt.,  in  an  assay  of  20  dwt. 

Mixing  with  Flux.  —  The  weighed    portions  of    an  ore    are 


ASSAY  OF  A  TYPICAL  SILICEOUS   ORE  337 

commonly  mixed  with  the  flux  on  a  sheet  of  glazed  paper,  using 
a  spatula  to  obtain  a  uniform  mixture.  The  charge  may  then  be 
readily  transferred,  to  a  clay  crucible  of  suitable  size,  and  the  paper 
swept  clean  by  a  small  flat  brush.  Another,  perhaps  preferable, 
method  is  to  mix  flux  and  ore  in  a  smooth  porcelain  mortar,  large 
enough  to  enable  the  mixture  to  be  stirred  freely.  In  many  assay 
offices  the  ore  and  flux,  after  mixing,  are  wrapped  in  thin  tissue 
paper  (Japanese  copying-paper  answers  the  purpose),  arid  the 
little  bundle  placed  in  a  crucible  which  has  been  previously  heated. 
The  fusion  in  this  way  is  probably  more  rapid  than  when  the  charge 
is  added  to  a  cold  crucible;  but  there  are  objections  to  the  method, 
as  will  be  shown  later. 

The  Fusion  Process.  —  The  assay  fusions  are  generally  carried 
out  in  small  square  furnaces  (8  in.  to  12  in.  square,  inside  measure- 
ment), capable  of  holding  from  2  to  6  crucibles  at  a  time,  and 
provided  with  horizontal  or  inclined  sliding  covers.  The  fur- 
naces and  such  parts  of  the  flue  as  are  exposed  to  strong  heat  are 
lined  with  fire-brick.  The  crucibles  should  be  firmly  supported 
on  fire-bricks  resting  on  the  bars  at  the  bottom,  but  arranged 
in  such  a  way  that  they  may  be  uniformly  heated  all  round;  and 
the  mouths  of  the  crucibles  should  not  be  at  a  higher  level  than 
the  opening  of  the  flue.  When  charcoal  is  used,  the  crucibles, 
after  putting  on  the  fire-clay  lids,  may  be  entirely  covered  by  a 
layer  of  fuel.  With  coke  it  is  hardly  necessary  to  use  a  support 
beneath  the  crucibles.  The  bars  of  the  furnace  must  be  clear 
of  ash  before  setting  the  crucibles  in  their  places. 

The  operation  of  fusion  usually  takes  afrout  40  minutes.  For 
the  first  10  minutes  or  so  the  temperature  should  be  kept  down 
to  avoid  loss  through  the  violent  expulsion  of  carbonic  acid,  water 
vapor,  etc.  At  this  stage,  signs  of  fusion  generally  begin  to 
appear  at  the  sides,  and  the  lids  had  better  be  removed,  provided 
the  fuel  is  burning  quietly  and  there  is  no  danger  of  lumps  of 
charcoal,  etc.,  being  projected  into  the  pots.  A  semi-fused  crust 
sometimes  forms  on  the  surface,  which  may  occasionally  be  raised 
nearly  to  the  mouth  of  the  crucible  by  the  action  of  gases  beneath, 
but  if  the  proper  conditions  be  observed  this  crust  soon  sinks 
down  and  no  projection  of  the  contents  from  the  crucible  takes 
place.  As  soon  as  the  action  begins  to  moderate,  the  temperature 
may  be  raised  (by  opening  the  damper  more  fully  and  closing 
the  covers  of  the  furnace) ,  and  the  heat  is  continued  until  all  signs 


338  THE  CYANIDE  HANDBOOK 

of  ebullition  have  ceased.  The  lids  are  then  replaced  for  the 
last  five  to  ten  minutes,  after  which  the  contents  should  be  ready 
to  pour.  A  fairly  bright  red  heat  is  needed  for  the  fusion,  but 
very  intense  heat  is  neither  necessary  nor  desirable. 

Fusions  in  the  Muffle.  —  The  fusions  are  sometimes  made  by 
placing  the  crucibles  in  a  large  muffle,  and  with  care  good  results 
can  be  obtained;  but  the  method  has  the  disadvantage  that  the 
actions  going  on  cannot  be  easily  observed  and  controlled;  also, 
with  poor  ores,  either  a  very  large  muffle  must  be  used  to  accom- 
modate the  large  crucibles  which  are  necessary,  or  a  number  of 
assays  on  each  sample  must  be  combined,  which  is  laborious  and 
troublesome. 

Pouring.  —  When  ready  for  pouring,  the  contents  of  the  cru- 
cible should  be  quite  tranquil;  the  crucibles  are  then  lifted  out 
of  the  furnace  by  means  of  iron  tongs,  bent  at  the  points  so  as  to 
grip  the  edge  of  the  crucible  firmly,  and  the  molten  contents 
poured  into  iron  molds,  previously  cleaned  and  slightly  warmed. 
The  fused  mass  should  pour  freely,  like  oil,  and  should  leave  no 
metal  or  lumps  of  any  kind  in  the  crucible,  which,  when  cool, 
should  show  internally  only  a  thin  layer  of  slag. 

Hammering  Lead  Buttons.  —  The  molds  are  left  about  five 
minutes  to  cool,  then  inverted,  and  the  slag  removed  from  the 
buttons  of  lead  by  one  or  two  blows  with  a  hammer.  No  shots 
or  detached  particles  of  lead  should  appear  in  the  slag,  but  in 
all  cases  it  should  be  carefully  examined,  and  any  detached  lead 
added  to  the  main  button.  The  color  and  appearance  of  the  slag 
will  depend  largely  on  the  nature  of  the  ore;  also  to  some  extent 
on  the  time  and  temperature  of  fusion.  When  the  ore  consists 
chiefly  of  silica,  with  small  quantites  of  oxide  of  iron,  as  in  the 
case  we  are  considering,  the  color  will  be  light  green;  with  large 
amounts  of  iron  it  will  be  dark  brown,  almost  black.  When 
copper  is  present  a  characteristic  reddish-brown  color  is  produced 
(due  to  cuprous  oxide).  The  lead  should  be  easily  detached 
from  the  slag,  and  should  not  leave  a  scale  or  film  behind  on 
breaking  off;  this  takes  place  sometimes  when  the  slag  is  exces- 
sively hard  and  stony,  as  may  be  the  case  if  too  much  borax  or 
acid  flux  has  been  used.  Often  the  slag  is  very  brittle  and  flies 
to  pieces  with  some  violence  on  merely  touching  with  a  hammer. 
The  hammering  should  be  done  on  a  steel  block,  mounted  on  a 
firm  wooden  support  and  surrounded  on  three  sides  by  a  frame 


ASSAY  OF  A  TYPICAL  SILICEOUS   ORE  339 

to  retain  flying  particles.  Hammer  and  anvil  faces  should  be 
kept  carefully  cleaned.  The  detached  lead  buttons  are  held  in 
steel  forceps  and  struck  on  the  edges  before  hammering  the  upper 
and  lower  surfaces,  otherwise  particles  of  slag  may  be  hammered 
into  the  block  of  lead,  causing  spitting  and  loss  in  cupellation. 
By  hammering  at  the  edges  and  brushing  the  lower  surface 
(where  the  button  was  in  contact  with  the  slag)  with  a  wire  brush, 
the  lead  may  be  effectually  cleaned.  The  block  of  lead  is  then 
beaten  into  a  roughly  cubical  shape,  and  placed  in  a  compart- 
ment of  a  cupel  tray. 

Arrangement  of  Assays.  —  In  working  a  batch  of  assays  it 
is  very  necessary  to  arrange  them  systematically  and  to  adhere 
to  the  same  order  of  arrangement  at  every  stage  of  the  process. 
Each  sample  is  first  marked  with  a  number,  and  the  same  number 
entered  in  the  assay  book,  with  sufficient  description  for  identi- 
fying the  sample  with  certainty.  In  placing  the  crucibles  in 
the  fusion  furnace,  the  lead  buttons  on  the  cupel  trays,  or  in  the 
muffle  for  cupellation,  etc.,  these  numbers  are  taken  in  the  order 
of  the  words  on  a  page  of  a  book.  Thus,  12  assays  in  2  fusion 
furnaces  might  be  arranged: 


Furnace  No.  1 

1  2  3 

456 


Furnace  No.  2 


789 
10  11  12 


When  subsequently  transferred  to  the  cupel  tray  they  might 
be  placed  thus: 

1234 
5678 
9  10  11  12 

If  this  principle  be  strictly  adhered  to,  no  confusion  or  am- 
biguity can  occur,  even  if  the  crucibles,  cupels,  etc.,  be  not 
actually  marked. 

It  is  a  good  plan  to  arrange  the  samples  so  that  the  lower- 
grade  assays  (e.g.,  cyanide  residues)  are  made  first.  The  same 
crucibles  may  then  be  used  for  the  richer  samples  without 
danger  of  "  salting  "  should  any  lead  remain  in  the  crucible  from 
a  previous  imperfect  fusion,  as  this  could  hardly  contain  a  weigh- 
able  quantity  of  gold. 

Fusion  in  Hot  Crucibles.  —  The  method  of  adding  fresh  charges 


340  THE   CYANIDE   HANDBOOK 

immediately  to  the  hot  crucibles,  whether  these  charges  are 
wrapped  in  paper  or  not,  is  not  to  be  recommended,  as  it  results 
in  very  violent  and  rapid  action  in  the  early  stages,  giving  rise 
very  probably  to  loss  of  material  through  ejection  of  particles 
from  the  crucible.  It  is  also  possible  that  the  lead  particles  will 
form  and  sink  to  the  bottom  of  the  crucible  before  the  siliceous 
matter  is  properly  fused,  and  that  particles  of  precious  metal 
will  therefore  remain  in  suspension  in  the  slag  without  ever  com- 
ing in  contact  with  lead.  When  the  temperature  is  kept  low  in 
the  early  stages  the  action  is  more  moderate;  the  lead  formed 
sinks  gradually  through  the  mass  and  has  a  better  chance  of  secur- 
ing all  the  particles  of  precious  metal. 

(B)    CUPELLATION    AND    PARTING 

Cupellation.  —  This  process  depends  upon  the  fact  that  when 
an  alloy  of  gold  and  silver  with  lead  is  heated,  with  free  access  of 
air,  in  contact  with  certain  porous  materials,  such  as  finely  pow- 
dered bone-ash,  the  lead  oxidizes,  this  oxide  being  partly  volatil- 
ized and  partly  absorbed  by  the  substance  on  which  it  rests; 
while  the  gold  and  silver  undergo  little  or  no  oxidation,  but,  after 
all  the  lead  has  disappeared,  remain  behind  in  the  form  of  a  nearly 
spherical  bead  of  fine  metal. 

Muffle- Furnaces.  —  The  operation  is  generally  carried  out  in 
a  small  fire-clay  oven,  called  a  "  muffle,"  consisting  of  an  oblong 
floor  surmounted  by  an  arched  roof  and  closed  at  one  end.  This 
is  supported  within  an  outer  furnace  ("muffle-furnace"),  so 
arranged  that  fuel  may  be  placed  below,  above,  and  on  both 
sides  of  the  muffle.  The  latter  is  at  least  partially  open  in  front, 
and  the  semicircular  end  is  usually  provided  with  a  slit  to  secure 
a  draft.  Slits  are  also  sometimes  made  in  the  sides  of  the  arch. 
Coal,  charcoal,  gas,  or  oil  are  used  as  fuel. 

Cupels.  —  The  "  cupels "  in  general  use  are  small  cylinders 
of  porous  material  with  a  hollow  at  one  end  for  the  reception  of 
the  lead  button.  Formerly,  they  were  always  made  of  bone- 
ash,  but  at  the  present  day  various  refractory  materials,  such 
as  magnesia  and  magnesium  borate,  have  been  applied  with  some 
success  in  the  manufacture  of  cupels. 

The  efficiency  of  bone-ash  cupels  depends  largely  on  the  amount 
of  water  added,  the  method  of  molding  and  pressing,  the  fineness 
and  purity  of  the  bone-ash,  and  the  time  of  drying  the  cupels 


ASSAY  OF  A  TYPICAL  SILICEOUS   ORE  341 

before  use.  Some  assayers  add  small  quantities  of  alkaline  car- 
bonates and  other  ingredients,  but  the  general  opinion  seems  to 
be  that  with  pure  bone-ash  the  best  results  are  obtained  by 
moderately  fine  crushing,  using  only  distilled  water.  The  amount 
of  water  should  be  only  just  sufficient  to  cause  the  material  to 
cohere,  and  not  sufficient  to  make  it  pasty.  The  cupels  are  then 
made  by  means  of  a  mold  consisting  of  a  hollow  metal  cylinder, 
which  is  filled  with  the  moist  bone-ash;  the  plunger  is  then  pushed 
in  and  struck  once  or  twice  with  a  mallet.  The  mold  is  then  in- 
verted and  the  cupel  turned  out.  Better  results  can  in  general 
be  obtained  by  the  use  of  manufactured  cupels,  which  are  much 
more  uniform  in  quality  than  can  be  the  case  with  those  made 
by  hand  on  the  spot.  Previous  to  use,  the  cupels  should  be  dried 
for  a  long  time  in  a  moderately  warm  place. 

Charging  into  Muffle.  —  The  cupels  are  placed,  empty,  in  the 
muffle,  in  rows  of  3  or  4,  as  may  be  convenient,  with  the  hollow 
uppermost.  After  about  10  minutes,  with  a  good  fire,  they  will 
begin  to  show  a  red  heat,  and  the  lead  buttons  may  then  be  added 
by  means  of  suitably  shaped  cupel  tongs,  each  button  being  care- 
fully placed  in  the  hollow  of  its  corresponding  cupel.  It  is  a 
good  plan  to  begin  by  adding  the  front  row  (i.e.,  the  row  nearest 
the  mouth  of  the  mu  ffle) ,  as  these  are  generally  cooler  than  the 
rest,  and  require  more  time  to  complete  the  cupellation,  The  other 
rows  are  then  added  in  succession  from  front  to  back.  The  num- 
ber of  assays  to  be  cupeled  simultaneously  will  depend  on  the 
size  of  the  furnace  and  of  the  cupels,  but  it  is  not  a  good  plan  to 
crowd  too  many  into  the  muffle  at  one  time;  if  the  furnace  be 
heated  sufficiently  to  cupel  the  front  row  in  a  full  muffle,  some  of 
the  back  rows  may  be  much  overheated,  leading  to  heavy  losses 
by  volatilization. 

Size  and  Form  of  Cupels.  —  The  size  of  cupels  to  be  used  will 
depend  on  the  weight  of  the  lead  buttons.  It  is  generally  assumed 
that  a  bone-ash  cupel  will  absorb  its  own  weight  of  lead.  For 
buttons  of  20-25  grams,  the  size  known  as  No.  7  is  convenient; 
for  15  grams,  No.  5  may  be  used.  The  depth  of  the  hollow  is 
also  of  some  importance.  If  too  shallow,  the  molten  lead  may 
overflow,  although  there  may  be  sufficient  absorbent  material; 
if  too  deep,  the  oxidation  proceeds  very  slowly  and  the  losses  of 
gold  and  silver  by  volatilization  may  be  heavy.  A  layer  of  bone- 
ash  should  be  placed  on  the  floor  of  the  muffle,  as  a  precaution 


342  THE  CYANIDE   HANDBOOK 

against  accidents  and  to  keep  the  litharge  from  attacking  the 
fire-clay  if  it  should  soak  through  the  bottoms  of  the  cupels. 

Process  of  Cupellation.  —  When  the  lead  buttons  are  placed 
on  the  cupels,  in  a  few  moments  the  lead  melts,  and  the  surface 
shortly  afterward  brightens  and  begins  to  exhibit  a  rotary  move- 
ment. This  bright  appearance  continues  until  the  operation  is 
complete,  provided  a  sufficient  temperature  be  maintained. 
When  the  operation  is  finished  the  movement  ceases,  but  the 
bead  of  gold  and  silver  may  remain  molten  for  some  time.  When 
drawn  forward  to  a  cooler  part  of  the  muffle,  it  suddenly  solidifies, 
emitting  a  bright  glow  of  light;  if  cooled  too  rapidly  particles  of 
metal  may  be  projected  onto  the  edges  of  the  cupel  or  entirely 
lost.  This  action  is  generally  Ascribed  to  the  expulsion  of  absorbed 
oxygen  as  the  silver  solidifies.  Large  buttons  exhibit  a  play  of 
iridescent  interference  colors  a  few  moments  before  the  finish  of 
the  operation.  At  a  suitable  temperature,  a  button  of  lead 
weighing  25  grams  will  be  cupeled  in  about  half  an  hour. 

Effects  of  Varying  Temperature.  — •  If  the  temperature  of  the 
muffle  during  cupellation  sinks  below  the  melting-point  of  litharge, 
a  crust  forms  on  the  buttons  and  the  movement  ceases.  This 
is  spoken  of  as  "  freezing."  When  this  has  taken  place  it  requires 
a  much  higher  temperature  to  re-start  the  cupellation,  and  there 
is  always  a  possibility  of  loss  in  doing  so.  The  temperature 
required  to  start  cupellation  and  also  to  complete  the  final 
stages  is  considerably  higher  than  that  required  to  maintain 
the  operation  during  the  earlier  part,  after  it  has  once  started. 
Losses  both  of  gold  and  silver  occur  in  all  cases,  by  volatilization 
and  by  absorption  in  the  cupels,  and  as  these  losses  are  increased 
by  rise  of  temperature,  an  accurate  assay,  especially  where  the 
determination  of  silver  is  of  importance,  is  always  conducted 
at  the  lowest  temperature  which  can  be  used  without  danger  of 
freezing. 

When  the  cupellation  has  been  carried  out  at  a  fairly  low 
temperature,  the  bead  at  the  finish  is  surrounded  by  a  ring  of 
feathery  yellowish  crystals  of  litharge. 

Losses  of  Gold  and  Silver  in  Cupellation.  —  According  to 
Hillebrand  and  Allen,1  "when  cupellation  takes  place  at  a  low 
temperature,  with  formation  of  considerable  feather  litharge, 
the  loss  by  volatilization  is  practically  negligible,  or  at  any  rate 

i  Bull.  No.  253,  U.  S.  G.  Survey  (1905). 


ASSAY  OF  A  TYPICAL  SILICEOUS   ORE  343 

is  perhaps  compensated  by  retention  of  lead;  but  when  the  cupella- 
tion  is  made  at  a  higher  temperature,  the  loss  is  considerable. " 
The  following  average  losses  were  determined  by  them  in  samples 
of  telluride  ore,  by  assaying  the  slags  from  the  original  fusions 
and  the  cupels  respectively.  The  results  give  the  amounts  of  gold 
and  silver  together  per  assay. 

In  Slags:  In  Cupels: 

Sample  Milligram  Milligram 

1 055  .085 

2 08  .10 

3 145  .16 

4 05  .18 

This  cupellation  loss  is  the  amount  absorbed,  and  does  not  in- 
clude the  loss  by  volatilization.  The  latter  could  only  be  deter- 
mined by  making  a  check  assay  with  known  quantities  of  gold 
and  silver  under  conditions  of  temperature,  etc.,  as  nearly  as 
possible  identical  with  those  of  the  actual  assay.  Experiments 
made  by  Hillebrand  and  Allen1  showed  that,  contrary  to  the 
usual  opinion,  the  losses  of  gold  in  cupellation  are  not  negligible, 
especially  with  rich  ores.  Tests  made  by  cupeling  various 
known  weights  of  gold  and  silver  with  25  grams  of  lead  in  each 
case,  to  correspond  with  an  ordinary  assay  button,  led  to  the 
following  conclusions: 

(1)  That  the  losses  of  gold  and  silver  increase  progressively 
from  front  to  back  of  muffle. 

(2)  That,  for  equal  amounts  of  gold,  the  loss  is  greater,  with 
25  grams  of  lead  than  with  5  grams. 

(3)  That  the  percentage  of  loss  of  gold  is  greater  with  small 
than  with  large  amounts  of  gold,  especially  in  the  hotter  part  of 
the  muffle. 

(4)  That  the  loss  of  gold  by  absorption  is  much  greater  than 
the  loss  by  volatilization;  when  no  silver  is  present  the  loss  is 
chiefly  due  to  absorption. 

(5)  That  the  loss  of  gold  is  about  the  same  whether  silver  is 
present  or  not. 

They  insist  on  the  necessity  for  corrected  assays  where  accu- 
rate results  are  required,  and  state  that  the  most  exact  results 
are  obtained  when  feather  litharge  is  still  abundant  at  the  time 
of  brightening. 


344  THE  CYANIDE  HANDBOOK 

Miller  and  Fulton  1  state  that  the  absorption  of  silver  by  the 
cupel  increases  with  the  size  of  button,  but  the  amount  absorbed 
per  gram  of  lead  button  cupeled  diminishes  regularly  as  the  lead 
increases.  They  find  also  that  the  loss  in  diminishing  a  lead 
button  by  scorification  is  irregular,  but  usually  greater  than  by 
cupeling  direct.  The  corrections  never  account  for  the  whole 
of  the  loss  of  silver. 

F.  P.  Dewey  2  remarks:  "While  the  correction  for  slag  and 
cupel  loss  is  easily  made,  and  ought  always  to  be  made  when 
accurate  statistics  are  kept,  there  is  yet  the  volatilization  loss  to 
correct,  and  some  means  of  doing  this  is  very  desirable.  While 
a  check  assay  answers  very  well  for  bullion,  it  would  hardly  be 
possible  to  construct  check  material  for  the  varying  characters 
of  ores  and  products  ordinarily  met  with." 

W.  P.  Mason  and  J.  W.  Bowman  3  give  a  table  showing  a 
number  of  results  of  losses  of  gold  and  silver  on  weighed  quan- 
tities, when  scorified  and  cupeled  in  a  Battersea  F  muffle,  the 
conditions  under  which  the  assays  were  made,  such  as  heat  of 
muffle,  draft,  and  manipulations  in  general,  being  such  as  would 
obtain  in  careful,  practical  work.  The  average  of  their  results 
show: 

TABLE  IV.  —  SCORIFICATION  AND  CUPELLATION  LOSSES  IN  A 
BATTERSEA  F  MUFFLE 


PERCENTAGE  Loss 

Silver 

Gold 

In  Scorification. 

0.55 
1.99 

0.574 
0.296 

In  Cupellation  

For  entire  process 

2.54 

0.87 

The  methods  of  assaying  slags  and  cupels  will  be  discussed  in 
a  later  section. 

Cleaning  and  Weighing  Fine  Metal.  —  When  the  cupels  are 
sufficiently  cool,  the  beads  of  fine  metal  (gold  and  silver)  are 
removed  by  means  of  a  small  pair  of  pliers,  pressed  tightly,  and 
if  large  enough  brushed  with  a  wire  scratch  brush,  then  hammered 

i"Sch.  Mines  Quart.,"  XVII,  p.  160  (1896). 

2"  Journ.  Am.  Chem.  Soc.,"  XVI,  p.  505. 

a"  Journ.  Am.  Chem.  Soc.,"  XVI,  p.  313  (Oct.  6,  1893). 


ASSAY  OF  A  TYPICAL  SILICEOUS   ORE  345 

on  a  smooth  clean  anvil  with  a  clean  smooth-faced  hammer. 
The  flattened  beads  may  conveniently  be  transferred  to  small 
porcelain  crucibles,  arranged  on  a  cupel  tray  or  wooden  frame, 
in  the  same  order  as  the  cupels.  They  are  then  weighed  on  the 
assay  balance.  For  ordinary  work  it  is  quite  sufficient  to  weigh 
the  fine  metal  within  .05  or  even  .1  mg.,  as  the  variations  in  the 
losses  of  silver  in  different  parts  of  the  muffle  probably  exceed 
this  amount. 

Inquartation.  —  In  cases  where  the  amount  of  silver  present 
is  less  than  2^  times  that  of  the  gold,  the  latter  protects  the 
silver  to  some  extent  from  the  action  of  the  nitric  acid  in  the 
subsequent  operation  of  parting.  When  this  is  the  case  it  will 
be  necessary  to  add  a  small  quantity  of  silver  foil,  a  milligram  or 
two  in  excess  of  the  amount  theoretically  required,  wrap  the 
bead  and  extra  silver  in  a  small  piece  of  lead-foil,  and  cupel  in  a 
small  cupel  (say  No.  3  size).  A  better  plan,  however,  is  to  make 
two  assays  of  the  material  —  one  without  adding  silver,  and  the 
other  with  the  necessary  silver  for  parting  added  to  the  flux  before 
transferring  to  the  crucible.  It  is  advisable  to  examine  the  silver- 
foil  used  and  make  sure  that  it  is  absolutely  free  from  gold. 

Parting.  —  This  operation  may  be  carried  out  either  in  porce- 
lain crucibles  or  in  small  long-necked  glass  flasks.  The  former 
method  is  quite  satisfactory,  and  if  carefully  carried  out  requires  less 
manipulation  and  trouble  than  the  method  with  parting-flasks. 

The  acid  required  for  parting  the  beads  from  ordinary  ore 
assays  is  nitric  acid,  20  per  cent,  by  volume — -i.e.,  a  mixture  of 
20  parts  pure  acid  (say  1.42  sp.  gr.)  with  J80  parts  distilled  water. 
From  10  to  15  c.c.  of  acid  are  required  for  each  bead.  The  cru- 
cibles are  4  to  4.5  cm.  in  diameter,  and  when  this  quantity  of 
acid  is  added  are  filled  about  two- thirds  full.  The  crucibles 
may  be  conveniently  arranged  on  a  perforated  metal  plate  sup- 
ported over  a  uniform  and  moderate  source  of  heat;  an  oil-stove 
with  large  wicks  can  be  used,  but  the  heat  is  not  really  uniform 
in  all  parts.  The  acid  must  be  heated  to  boiling,  but  not  allowed 
to  boil  too  violently,  as  in  some  cases  the  beads  may  break  up 
and  pieces  of  gold  may  be  projected  from  the  crucibles  and  lost. 
The  heating  must  be  continued  until  no  signs  of  red  fumes  can 
be  observed,  and  until  no  further  evolution  of  small  bubbles  takes 
place.  Care  must  be  taken  not  to  allow  the  liquid  to  evaporate 
to  dryness. 


346  THE  CYANIDE  HANDBOOK 

With  ordinary  assay  beads  a  second  parting  is  hardly  neces- 
sary. With  large  beads,  however,  it  is  advisable  to  pour  off  the 
first  (weak)  acid  and  add  an  equal  amount  of  a  stronger  acid 
(50  per  cent,  by  volume).  This  is  heated  to  boiling  and  again 
poured  off  when  the  action  appears  to  be  finished.  The  crucible 
is  then  filled  up  with  distilled  water,  which  is  carefully  decanted; 
if  the  gold  has  broken  up,  as  will  be  the  case  when  a  large  excess 
of  silver  was  present,  this  operation  requires  close  attention,  and 
it  is  best  to  pour  the  water  off  along  a  glass  rod  into  a  porcelain 
basin.  After  washing  once  or  twice  in  this  way,  the  crucibles  are 
dried  slowly  to  avoid  spurting:  generally  this  may  be  safely  done 
by  setting  them  on  the  perforated  frame  in  a  slightly  inclined 
position  and  turning  the  lamp  down.  They  are  finally  heated 
until  the  gold  acquires  its  natural  yellow  color.  When  cool  it  is 
ready  for  weighing. 

When  parting-flasks  are  used  they  are  generally  supported 
on  a  specially  constructed  frame  so  that  they  rest  in  a  slightly 
inclined  position;  this  is  heated  with  the  necessary  precautions 
against  bumping  and  spurting.  After  pouring  off  the  acid  the 
flask  is  filled  to  the  top  with  distilled  water  and  inverted  into  a 
small  crucible  of  unglazed  porous  material  (annealing-cup). 
This  may  easily  be  done  without  spilling  any  liquid  by  placing 
the  crucible  over  the  mouth  of  the  flask  before  inverting  the  latter. 
The  gold  then  sinks  to  the  bottom  of  the  annealing  cup;  the  in- 
verted flask  is  gradually  raised,  allowing  the  cup  to  fill  with  water, 
the  flask  is  then  withdrawn  by  a  quick  lateral  movement  and 
the  surplus  water  poured  off.  For  small  beads,  test-tubes  may 
preferably  be  used  instead  of  parting-flasks.  Generally  speak- 
ing, this  method  is  more  troublesome  than  parting  in  crucibles. 
A  glazed  porcelain  crucible  may  of  course  be  used  instead  of  the 
porous  annealing-cup,  and  is  perhaps  preferable,  as  small  particles 
are  liable  to  chip  off  the  edges  of  the  latter  and  might  occasion 
errors  in  weighing  broken  gold,  but  greater  care  is  necessary  in 
drying  the  gold  in  a  glazed  crucible. 

Purity  of  Parting  Acid.  —  Care  must  be  taken  that  the  nitric 
acid  used  is  free  from  chlorides,  free  chlorine,  hydrocyanic  acid, 
or  any  impurity  which  could  precipitate  silver  in  acid  solution 
or  dissolve  gold,  either  by  itself  or  in  conjunction  with  nitric 
acid.  Silver  nitrate  added  to  the  diluted  parting  acid  should  give 
no  turbidity.  If  any  milkiness  be  observed,  it  is  best  to  add  a 


ASSAY   OF  A  TYPICAL  SILICEOUS   ORE  347 

certain  quantity  of  silver  nitrate  to  all  the  parting  acid  made 
up  from  that  lot  of  strong  acid,  and  to  allow  the  turbidity  to  settle 
before  using.  Nitrous  acid  has  generally  been  considered  to  be 
a  solvent  for  gold;1  but  the  researches  of  Hillebrand  and  Allen2 
would  appear  to  show  that  this  acid  has  no  such  action.  Nitrous 
acid  is  shown  by  a  reddish  brown  color  and  by  the  dilute  acid 
liberating  iodine  from  potassic  iodide  (test  with  starch  solution). 
The  same  writers  also  found  no  evidence  of  the  solution  of  gold 
by  prolonged  boiling,  in  pure  nitric  acid.  There  is,  however,  some 
reason  for  believing  that,  under  conditions  not  clearly  under- 
stood, a  quite  perceptible  quantity  of  gold  may  be  dissolved, 
so  that  the  assayer  will  do  well  to  use  the  purest  acid  obtainable 
and  avoid  prolonging  the  process  of  boiling  after  the  action  on 
the  silver  has  entirely  ceased. 

The  distilled  water  used  must  of  course  also  be  free  from  any 
impurities  which  might  precipitate  silver,  act  on  the  gold,  or 
otherwise  interfere  with  the  process. 

Adjustment  of  Assay  Balance.  —  Before  weighing  a  batch  of 
gold  assays  it  is  essential  to  verify  the  adjustment  of  the  assay 
balance.  The  case  should  be  free  from  dust,  inside  and  out, 
and  the  plate  on  which  the  balance  rests  should  be  quite  level, 
usually  shown  by  two  small  spirit-levels  placed  at  right  angles 
inside  the  balance  case.  If  necessary,  it  must  be  leveled  by 
raising  or  lowering  the  supporting  screws.  If  the  balance  is 
much  out  of  adjustment,  it  is  rectified  by  moving  the  vane  or 
adjusting  screw  in  the  required  direction.  Small  variations  in 
adjustment  are  best  corrected  by  means  of  a  rider.  If  the  right 
arm  of  the  balance  be  used  for  the  weights,  as  is  generally  the 
case,  the  adjusting  rider  may  conveniently  be  placed  on  the  left 
arm,  which  is  kept  permanently  one-  or  two-tenths  of  a  mg. 
lighter  than  the  right  arm.  Any  small  variation  of  adjustment 
occurring  during  the  course  of  weighing  (due  to  differences  of 
temperature,  etc.)  can  thus  be  corrected  by  moving  the  left- 
hand  rider,  without  any  disturbance  of  the  balance. 

Weighing  Parted  Gold.  —  The  crucibles  or  annealing-cups 
containing  the  parted  gold  are  arranged  in  their  proper  order 
on  a  cupel  tray,  or  on  any  suitable  frame  which  allows  them  to 
be  moved  simultaneously.  The  gold  is  then  transferred  from 

iG.  H.  Making,  in  "  Journ  Chem.  Soc.,"  XIII,  p.  97  (1861). 
2  Bull.  No.  253,  U.  S.  G.  Survey  (1905). 


348 


THE  CYANIDE   HANDBOOK 


the  crucible  to  the  balance  pan  by  means  of  a  needle  or  very 
fine  camel's-hair  brush;  sometimes  a  slight  tap  may  be  needed  to 
move  it.  The  pan  should  be  placed  on  a  sheet  of  glass  or  a  smooth 
card,  so  that  any  loose  particles  which  might  be  lost  in  transfer 
may  be  at  once  seen.  A  good  balance  will  determine  the  weight 
within  .01  mg.,  which  is  sufficient  for  most  purposes,  this  amount 
corresponding  to  4.8  grains  per  ton  (20  cents  gold  value)  on  an  as- 
say of  1  assay  ton,  or  2.4  grains  (10  cents)  on  an  assay  of  2  assay  tons. 

Most  balances  are  so  constructed  that  weights  less  than  0.05 
mg.  and  weights  lying  between  0.9  and  1.0  mg.  cannot  be  con- 
veniently weighed  with  the  rider  alone.  In  such  cases  a  counter- 
poise of  known  weight  (say  0.5  mg.)  may  be  placed  in  the  pan,  or 
the  left-hand  rider  may  be  moved  one  or  more  divisions,  so  that 
the  zero-point  in  weighing  is  no  longer  at  the  center  of  the  beam, 
care  being  taken  to  return  the  rider  to  its  normal  position  after 
each  such  weighing. 

After  weighing,  the  gold  should  be  immediately  transferred 
to  a  small  cup  or  other  vessel  placed  in  the  balance  case,  so  that 
the  accumulated  beads  may  be  recovered,  and  also  to  avoid  any 
risk  of  their  finding  their  way  into  other  samples. 

Reporting  Results.  —  A  convenient  method  of  recording  the 
assay  results  is  to  use  the  headings  here  shown: 


No. 
of 
Sample 

Description 

Date 

WEIGHT  FOUND 

ASSAY  OF  SAMPLE 

Gold  and 
Silver: 
mg. 

Gold: 
mg. 

Gold  : 
Dwt. 

Silver: 
Dwt. 

The  weights  of  fine  metal  in  milligrams  are  noted  in  the  column 
headed  "  Gold  and  Silver,"  and  the  weights  of  gold  are  subse- 
quently entered  in  the  next  column,  headed  "Gold:  mg."  The 
difference  of  these  entries  gives  the  weight  of  silver  in  milligrams. 
If  the  assay  be  on  1  assay  ton,  the  weights  of  gold  and  silver  in 
milligrams  must  be  each  multiplied  by  twenty  to  obtain  the 
assay  in  pennyweights.  If  the  assay  be  on  2  assay  tons,  they 
must  be  multiplied  by  ten. 


SECTION   III 

SPECIAL  METHODS  OF  ASSAY  FOR  PARTICULAR  ORES 
AND   PRODUCTS 

(A)  THE  SCORIFICATION  ASSAY 

Variable  Nature  of  Material  for  Assay.  —  The  ores  treated,  and 
the  materials  obtained  as  by-products  in  the  treatment  of  gold 
and  silver  ores  by  the  cyanide  process,  are  of  such  varied  nature 
that  no  single  method  of  assaying  is  applicable  in  all  cases.  When 
these  ores  or  materials  are  of  high  assay  value,  or  present  diffi- 
culties in  the  ordinary  method  of  assaying  as  described  in  the 
previous  section,  special  care  and  experience  are  required  in 
dealing  with  them.  In  doubtful  cases  it  is  always  well  to  try 
two  or  more  distinct  methods  on  the  same  sample.  The  agree- 
ment of  duplicate  assays  by  the  same  method  cannot  be  accepted 
as  a  proof  of  correctness,  as  experience  often  shows  that  a  different 
method  may  yield  a  totally  different  result. 

Scarification.  —  The  most  generally  applicable  method  for 
many  different  classes  of  material  is  scorification,  and  this  will 
be  first  considered.  As  a  rule  the  method  can  only  be  conveniently 
applied  to  comparatively  rich  ores  or  products,  as  the  amount 
taken  for  each  assay  of  the  substance  is  necessarily  small,  an 
ordinary  charge  being  5  to  8  grams.  In  exceptional  cases  as 
much  as  15-20  grams  may  be  taken,  but  this  involves  the  use  of 
large  scorifiers.  The  scorifiers  in  general  use  are  small  fire-clay 
dishes  varying  in  size  from  1^  in.  up  to  3  or  4  in.  in  diameter. 
The  substance  to  be  assayed  is  mixed  with  pure  lead  in  the  form 
of  small  grains,  and  placed  in  the  scorifiers.  The  general  custom 
is  to  mix  half  the  lead  with  the  material  to  be  scorified  and  add 
the  remainder  as  a  cover,  together  with  a  very  small  amount  of- 
borax  or  other  flux.  In  some  cases,  litharge  may  be  added  with 
advantage  instead  of,  or  as  well  as,  metallic  lead. 

The  following  five  charges  are  given  as  examples  for  ordinary 

349 


350 


THE  CYANIDE   HANDBOOK 


cases;  the  quantities  given  are  in  grams,  unless  otherwise  desig- 
nated : 


Charge  1 


Charge  2 


Charge  3 


Charge  4 


Charge  5 


Weight  of  material 

Grain  lead 

Litharge 

Fused  borax 

Silica 

Diam.  of  scorifier 


a.  t. 

50 


0.2 


5 

60 

0.25 
2  Jin. 


5 

30 

35 

0.25 

2 1  in. 


70 
0.25 


Sin 


ia.t. 

27 

22 
0.5 
0.4 

3  in. 


The  last  (No.  5)  is  suitable  for  pyritic  ore  or  similar  material. 
The  amount  of  silica  may  be  varied  according  to  the  quantity  of 
pyrites  present  in  the  ore.  In  this  case  the  litharge  and  silica 
are  to  be  mixed  with  the  ore  and  the  lead  and  borax  added  as  a 
cover. 

Charges  for  Material  Containing  Copper.  —  The  following  is 
suitable  for  material  containing  small  amounts  of  copper  and 
low-grade  in  precious  metals: 

Charge  6 

Material  for  assay 14^  grams  =  \  a.t. 

Grain  lead 60 

Fused  borax 0.05       " 

Scorifier 3^  in. 

For  highly  cupriferous  material: 

Charge  7 

Substance  for  assay 7.23          grams  =  \  a.t. 

Grain  lead     75 

Borax 0.2  to  0.3      " 

Scorifier     3^  in.  or  4  in. 

Charges  for  Rich  Silver  Ores.  —  For  rich  silver-bearing  material 
one  of  the  following  may  be  used: 

Charge  8  Charge  9 

Substance  for  assay ^  a.t.  ^V  a.t. 

Grain  lead 30-70  grams  40-60  grams 

Borax 0.3-3       "  0.5        " 

Scorifier     2^  in.  to  2f  in.  2^  in. 

Zinc-Box  Precipitate.  —  The  following  is  given  by  R.  W. 
Lodge  l  for  the  assay  of  zinc-box  precipitate : 

i  Trans.  A.  I.  M.  E.,  XXXIV,  p.  432  (October,  1903). 


SPECIAL  METHODS   OF  ASSAY 


351 


Charge  10 

Precipitate    0.05  a.t. 

Grain  lead     65  grams 

Borax  glass     10       " 

Scorifier  3  in.  or  4  in. 

35  grams  of  the  lead  to  be  mixed  with  the  material  and  30  grams  to  be  used 
as  cover 

Lead  Required  for  Scorifying  Different  Kinds  of  Material.  — • 
As  will  be  seen  by  the  above  figures,  the  amounts  of  grain  lead 
required  to  scorify  various  kinds  of  material  are  very  different, 
according  to  the  nature  of  the  material.  The  following  table 
gives  some  of  the  usually  accepted  figures  on  this  subject: 

TABLE  V.  —  GRAIN  LEAD  REQUIRED  WITH  VARIOUS  MATERIALS 


Nature  of  Material  Taken 

To  BE  ADDED  PER  GRAM  OF  MATERIAL  ASSAYED 

Lead  :   Grams 

Borax:    Grams 

Galena  

5-  8 
8-10 
8-10 

10-15 

12 
12-20 

16 
16-18 

0.1-0.15 
nil 
0.25-1 

0.1-0.2 

0.05 
0.1-0.15 

0.1-1 
0.1  (with  litharge  cover) 

Quartzose  ores  
Basic  ores 

Pyritic  ore    1 

Blende                             J 

Graphite  
Fahl  ore 

Arsenical  ore  ] 

Antimonial  ore          .    .  I 

Telluride  ore 

Mode  of  Procedure.  —  In  an  ordinary  scorification  assay,  the 
materials,  mixed  as  directed,  are  placed  in  the  hollow  of  the 
scorifier,  which  is  then  introduced  into  the  muffle  at  a  low  red 
heat.  In  many  cases  it  is  preferable  to  add  the  borax  little  by 
little,  as  the  action  proceeds.  The  temperature  is  then  raised 
gradually  to  bright  redness,  keeping  the  muffle  door  closed,  say, 
for  15  minutes,  by  which  time  the  mass  should  be  completely 
fused.  The  door  is  then  opened  sufficiently  to  give  a  good  current 
of  air,  when  litharge  is  rapidly  formed,  and  may  be  seen  forming 
a  ring  round  a  bright  central  spot  or  "eye."  This  spot  gradually 
diminishes  until  it  is  completely  covered  by  the  layer  of  molten 
slag.  The  temperature  is  now  again  raised,  by  closing  the  door 
or  increasing  the  draft.  At  this  stage  it  is  sometimes  a  good 


352  THE  CYANIDE  HANDBOOK 

plan  to  add  a  small  quantity  of  a  reducing  agent,  say  0.5  to  0.8 
part  of  anthracite  powder  to  every  100  parts  of  lead  originally 
taken.  This  is  wrapped  in  tissue  paper  and  placed  quickly  on 
top  of  the  slag;  it  serves  to  reduce  any  silicates  of  silver  that  may 
have  been  formed.  When  all  action  appears  to  have  ceased  and 
the  contents  of  the  scorifier  are  quite  liquid,  the  latter  is  removed 
from  the  muffle  by  means  of  "  scorifier "  tongs,  consisting  of  two 
arms,  the  upper  one  of  which  rests  across  the  top  of  the  scorifier 
while  the  lower  one  is  branched  in  U-shape,  so  as  to  hold  the  bottom 
of  the  scorifier  firmly.  While  the  scorifier  is  held  in  this  way  its 
contents  are  poured  into  a  dry,  clean  mold.  When  cool,  the  slag 
is  detached  and  the  lead  button  cleaned  for  cupellation.  The 
process  must  not  be  continued  too  long  after  the  "eye"  has 
closed,  i.e.,  after  the  lead  is  completely  covered  by  the  layer  of 
slag,  as  the  size  of  the  lead  button  gradually  diminishes,  and 
when  too  small  much  of  the  gold  and  silver  may  pass  into  the  slag. 

Remelting  Slag.  — •  In  any  case  it  is  advisable,  with  all  samples 
that  are  at  all  rich,  to  remelt  the  slag  with  fresh  flux.  This  may 
be  done  by  grinding  the  slag  in  a  mortar  and  fusing  in  a  clay 
crucible  with  20  grams  litharge,  2  grams  sodium  carbonate,  and 
1  gram  charcoal.  The  resulting  lead  button  is  cupeled  and  the 
result  obtained  added  to  that  from  the  scorification  assay;  or  the 
two  buttons  may  be  cupeled  together. 

Theory  of  Scorification  Assay.  —  The  theory  of  the  process  is 
described  by  J.  Daniell 1  as  follows: 

"  The  oxidation  of  lead  produces  litharge,  or  litharge  is  added 
with  the  charge.  With  the  silica  (of  the  scorifier  or  of  the  ma- 
terial assayed)  this  forms  the  extremely  fusible  silicate  Pb2SiO4. 
By  sulphides,  the  oxide  is  reduced  back  to  metallic  lead  with 
formation  of  sulphur  dioxide  in  presence  of  a  current  of  air,  and  a 
metallic  oxide  which  is  dissolved  by  the  excess  of  litharge.  In 
fact,  fused  litharge  is  an  extremely  powerful  solvent,  and  there 
are  very  few  substances  which  are  not  attacked  and  held  in 
1  igneous  solution ;  by  it.  The  noble  metals  are  thus  concentrated 
in  the  unoxidized  metallic  lead  and  are  subsequently  obtained  by 
cupellation." 

Inconveniences  of  Scorifying  in  Muffle.  —  With  ordinary 
muffle  furnaces  there  is  a  tendency,  already  noted,  for  the  back 
of  the  muffle  to  become  much  hotter  than  the  front;  hence  the 

i "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  277. 


SPECIAL  METHODS   OF  ASSAY  353 

scorifications  at  the  back  are  apt  to  finish  first,  and  where  large 
numbers  are  assayed  simultaneously  it  may  be  troublesome  to 
remove  these  at  the  proper  time  without  upsetting  or  interfering 
with  those  in  front. 

Scarification  Assay  in  Fusion  Furnace.  —  A  modified  form  of 
the  process,  described  by  Daniell,1  will  meet  this  difficulty.  The 
operation  is  carried  out  in  a  "Cornish  fire." 

"  Duplicate  trials  of  about  3  grams  of  ore  were  taken,  mixed  with  25  grams 
of  granulated  assay  lead  and  a  small  quantity  of  a  flux  composed  of  equal 
weights  of  carbonate  of  soda  and  borax.  Another  quantity  of  25  grams  gran- 
ulated lead  was  then  put  in  and  covered  with  a  further  quantity  of  flux.  The 
crucibles  were  placed  in  a  full  fire  at  a  low  heat  [small  wide-mouthed  crucibles 
were  used  instead  of  scorifiers],  with  damper  closed,  4,  6  or  more  at  a  time, 
depending  on  the  size  of  the  furnace.  When  melted,  the  bricks  were  opened, 
and  damper  raised,  causing  a  current  of  air  to  play  upon  the  crucibles,  ensuring 
rapid  oxidation  of  the  lead  and  a  thorough  scorification  of  the  ore.  .  .  .  The 
use  of  the  Cornish  fire  in  this  way  has  been  thoroughly  tested  and  gives  per- 
fectly satisfactory  results." 

Cautions.  —  T.  Kirke  Rose2  remarks,  in  reference  to  scorifica- 
tion: "Effervescence  and  spurting  may  occur,  especially  if  the 
scorifier  has  not  been  well  dried  by  warming  before  it  is  used." 

Daniell3  says:  "There  are,  of  course,  a  few  precautions  which 
have  to  be  taken.  For  instance,  pyritic  material,  especially 
arsenical  pyrites,  has  a  tendency  to  decrepitate,  throwing  out 
minute  particles  which  burn  with  a  characteristic  sparkle  and 
entail  loss.  This  can  be  obviated  by  careful  attention  to  the  heat 
at  the  commencement  of  the  operation.  Again,  carbonaceous 
matter  in  presence  of  litharge  generates  gas,  which,  rising  through 
the  melted  lead,  may  occasion  loss  by  projection  of  particles." 

Reduction  of  Large  or  Impure  Buttons.  —  It  sometimes  happens 
on  pouring  a  scorification  assay  that  the  button  of  lead  obtained 
is  too  large  to  be  conveniently  cupeled,  and  in  other  cases  it  may 
be  hard,  brittle,  or  coppery  in  appearance.  In  such  cases  the  slag 
should  be  removed  and  the  button  replaced  in  the  same  scorifier, 
fresh  lead  being  added  in  the  case  of  hard  or  impure  buttons. 
The  scorification  is  continued  until  the  button  is  reduced  to  the 
proper  size  for  cupellation  and  appears  quite  clean  and  malleable. 
According  to  Rose4  (loc.  cit.)  less  loss  of  the  precious  metals  is 
i  ibid. 

a"  Metallurgy  of  Gold,"  p.  383. 

3  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  277. 

4  Compare  Miller  &  Fulton,  "  Sch.  Mines  Quart.,"  XVII,  p.  160. 


354  THE  CYANIDE  HANDBOOK 

incurred  by  scorifying  lead  than  by  cupeling  it,  and  consequently 
it  is  better  to  reduce  any  lead  button  weighing  more  than  20 
grams  by  rescorification  before  cupellation. 

Assay  of  Graphite  Crucibles.  —  The  following  method  is  given 
by  T.  L.  Carter  1  for  assaying  graphite  crucibles  (i.e.,  old  pots  that 
have  been  used  for  smelting  operations) : 

"  A  quantity  not  exceeding  6-7  grains  (say  .4  to  .5  grams)  of 
the  finely  powdered  material  is  taken;  if  poor,  several  buttons 
are  combined.  The  bottom  of  a  large  scorifier  is  rubbed  with 
silica,  then  40  grains  (say  3  grams)  of  pure  litharge  is  introduced, 
followed  by  the  plumbago  arid  4  grains  (say  .25  gram)  of  niter. 
These  materials  are  mixed  together,  30  grains  (i.e.,  2  grams) 
litharge  added,  and  finally  a  covering  of  borax.  The  temperature 
is  kept  very  low  for  a  few  minutes,  then  gradually  raised  to  a  white 
heat  till  the  mass  fuses  completely.  As  a  check,  3  assays  are 
made  by  scorification  and  3  by  pot  fusion." 

Acid-Treated  Residues.  —  Scorifioation  is  also  used  sometimes 
for  assaying  the  residues  from  ores  and  other  products  which 
are  largely  soluble  in  acids,  as  certain  cupriferous  materials,  etc. 
This  will  be  referred  to  later. 

Limitations  of  Scorification  Assay.  —  Dr.  Loevy 2  observes: 
"  For  Rand  ores  and  for  all  kinds  of  tailings  and  slimes,  scorifica- 
tion is  entirely  out  of  the  question;  but  for  a  certain  class  of  ma- 
terial, such  as  graphite  crucibles,  certain  slags,  antimonial  ores, 
lead  ores,  etc.,  the  scorification  assay  is  the  only  reliable  one." 

This  statement  appears  a  little  too  sweeping,  especially  as 
regards  antimonial  and  lead  ores.  (See  below.) 

(B)  CRUCIBLE  FUSIONS  FOR  VARIOUS  CLASSES  OF  ORE 

Classes  of  Ore  for  Assay.  —  As  already  remarked,  the  flux  to 
be  used  must  always  be  adjusted  to  the  nature  of  the  ore,  and  no 
fixed  rules  can  be  given.  The  following  examples  may,  however, 
be  of  some  use  as  a  guide.  The  classes  which  will  be  here  con- 
sidered are: 

Class     I.   Siliceous  (Quartzose  Ores). 
Class   II.   Basic  (Oxidized)  Ores. 
Class  III.   Pyritic  Ores. 

» "  Eng.  and  Min.  Journ.,"  Aug.  5,  1899  (p.  155). 

a  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  206. 


SPECIAL  METHODS   OF  ASSAY  355 

Class    IV.   Lead-Zinc  Ores. 
Class      V.   Arsenical  Ores. 
Class     VI.    Antimonial  Ores. 
Class   VII.   Cupriferous  Ores. 
Class  VIII.  Telluride  Ores. 

Methods  of  Assay.  —  The  methods  of  assay  employed  may  be 
grouped  under  the  following  heads: 

(a)  Direct  fusion  with  ordinary  fluxes  (i.e.,  soda,  borax,  litharge 
and  charcoal,  or  substitutes  for  these). 

(b)  Direct  fusion  with  special  oxidizing  fluxes  (niter,  manganese 
dioxide,  etc.). 

(c)  Direct    fusion    with    a    desulphurizing    agent  —  generally 
metallic  iron. 

(d)  Fusion  after  preliminary  roast  or  oxidizing  process. 

(e)  Fusion  after  preliminary  wet  chemical  treatment. 

Class  I.  —  Siliceous  Ores 

Consisting  mainly  of  quartz,  with  very  small  quantities  of 
oxide  of  iron,  iron  pyrites,  calcium  and  magnesium  silicates  and 
carbonates,  etc.  The  quantity  taken  for  assay  will  vary  from 
J  assay  ton  up  to  4  assay  tons,  according  to  richness,  but  on  a 
cyanide  plant  it  is  seldom  desirable  to  use  less  than  1  assay  ton. 

Fluxes  for  Free-Milling  Ores.  —  We  give  here  a  number  of 
fluxes  adapted  from  those  recommended  by  different  writers,  so 
as  to  be  applicable  to  charges  of  1  assay  ton.  The  quantities  are 
given  in  grams: 

Flux  No.  1  No.  2          No.  3  No.  4  No.  5  No.  6 

Bicarbonate  of  soda 45-68  50  60  60  50  48 

Carbonate  of  soda 30-46  33  40  40  33  32 

Borax  glass 7-15  10  6  cover  nil  5 

Litharge 15-30  40  45  98  49.55  57 

Charcoal 1-1.5   as  required  1  0.45  1.1 

Flour 2.4 

Nearly  all  writers  on  assaying  give  bicarbonate  of  soda  in  the 
fluxes  recommended.  If  the  monocarbonate  (Na2CO3)  is  to  be 
used,  the  amount  Of  bicarbonate  should  be  reduced  in  the  pro- 
portion of  2  to  3;  thus  40  grams  Na.C03  are  equivalent  to  60 
grams  NaHCO3. 

Of  the  above  fluxes,  No.  1  is  based  on  the  recommendations  of 
T.  Kirke  Rose.1  The  quantities  there  given  are  "From  1  to  1J 

» "  Metallurgy  of  Gold,"  4th  edition,  p.  470. 


356  THE  CYANIDE  HANDBOOK 

assay  tons  of  soda  carbonate  and  from  J  to  J  assay  ton  of  borax 
to  1  assay  ton  of  ore."  And  with  regard  to  litharge  he  remarks: 
"Litharge  or  red  lead  is  added  in  the  proportion  of  one  or  two 
parts  to  two  of  ore;  if  too  much  litharge  is  used  the  slags  are  not 
clean,  as  a  slag  containing  lead  may  mean  a  loss  of  silver  and  gold." 
[The  amount  of  litharge  here  recommended  appears  to  be  much 
less  than  that  which  the  general  experience  of  assayers  shows  to 
be  desirable.  —  J.  E.  C.] 

No.  2  is  given  as  applicable  to  ordinary  quartz  ores  on  the  Rand, 
and  is  recommended  by  B.  W.  Begeer.1 

No.  3  is  adapted  from  the  flux  given  by  C.  and  J.  Beringer.2  As- 
suming the  reducing  power  of  charcoal  to  be  twice  that  of  flour,  we 
might  substitute  1.2  grams  charcoal  for  the  2.4  grams  flour  above. 

No.  4  is  a  flux  calculated  on  the  lines  of  that  given  by  C.  H. 
Fulton 3  for  the  production  of  a  "  sesquisilicate "  slag,  with  a 
charge  of  0.5  assay  ton.  The  amount  of  NaHCO3  is  doubled,  and 
the  litharge  is  calculated  on  the  assumption  that  76  grams  are 
required  for  the  slag  and  22  grams  to  give  a  20-gram  lead  button. 

No.  5  is  a  flux  recommended  by  G.  B.  Hogenraad4  for  the 
ore  at  Redjang  Lebong,  Sumatra,  which  is  practically  a  free- 
milling  ore,  but  contains  small  amounts  of  pyrites,  manganese 
peroxide,  copper,  and  selenium.  Borax  is  omitted,  as  it  was 
thought  to  carry  part  of  the  silver  into  the  slag. 

No.  6  is  the  flux  adopted  by  the  writer  for  free-milling  ores  of 
ordinary  types.  (See  Section  II,  A.) 

The  following  fluxes  are  adopted  in  a  similar  way  for  charges 
of  2  assay  tons: 

Flux  No.  1  No.  2  No.  3           No.  4                  No.  5 

Bicarbonate*  of  soda  .  . .  .  100  100  117           110                  85 

Carbonate  of  soda 07  67  78             73                  57 

Fused  borax 30  20  12                                    8 

Litharge      45  80  88             89.7             120 

Charcoal    -  as  required  0.3                 2 

Flour    -  4.7 

Argol    2.5 

Glass    -  20 

The  quantities  are  given  in  grams. 

No.  1  is  a  flux  formerly  used  in  the  assay  office  of  the  Robinson 
G.  M.  Company  of  Johannesburg;  it  was  found  to  give  lead  buttons 

i  "  Metallurgy  of  Gold  on  the  Rand,"  1898. 

2 "Text  Book  of  assaying,"  9th  edition,  p.  138. 

3"  A  Manual  of  Fire  Assaying,"  1907,  p.  66. 

4"  Journ.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  VIII,  73  (1907). 


SPECIAL  METHODS   OF  ASSAY  357 

of  about  20  grams,  with  a  clear  green  slag.  The  borax  seems 
excessive. 

No.  2  is  given  by  B.  W.  Begeer  *  for  tailings  on  the  Rand. 

No.  3  is  adapted  from  a  flux  given  by  C.  and  J.  Beringer,2  the 
quantities  there  given  for  50  grams  being  increased  in  the  pro- 
portion 58J :  50.  We  might  substitute  2.35  grams  of  charcoal 
for  the. 4. 7  grams  of  flour  above  given. 

No.  4  is  a  flux  recommended  by  G.  B.  Hogenraad  for  the  2 
assay  ton  charges  at  Redjang  Lebong.  It  is  said  to  give  lead 
buttons  of  30  grams,  with  a  clear  green  slag.  With  pure  siliceous 
ores  more  charcoal  would  be  necessary. 

No.  5  adopted  by  the  writer.     (See  Section  II,  A.) 

The  following  flux,  suitable  for  cyanide  tailings,  is  given  by 
C.  and  J.  Beringer,3  for  a  charge  of  3  assay  tons. 

Bicarbonate  of  soda 135  grams 

Carbonate  of  soda 90      " 

Borax 22       " 

Litharge 135       " 

Charcoal  as  required. 

The  writer  uses  the  following  for  charges  of  4  assay  tons,  the 
fusion  being  made  in  a  Battersea  No.  12  fluxing  pot. 


Bicarbonate  of  soda 161  grams 

Carbonate  of  soda 108      " 

Fused  borax 15.7  " 

Litharge 141      " 

Charcoal  .  2.3  " 


Total,  428  grams 


Probably  the  total  quantity  of  flux  per  charge  might  be  increased 
with  advantage,  but  in  that  case  a  larger  crucible  would  be  neces- 
sary. 

General  Remarks 

With  certain  classes  of  ore  the  amount  of  litharge  in  the  flux 
may  be  reduced  to  some  extent,  if  the  amount  of  soda  be  corre- 
spondingly increased,  and  vice  versa.  As  already  pointed  out, 
carbonate  of  soda  is  for  various  reasons  preferable  to  bicarbo- 
nate. (Section  II,  A.)  An  excessive  quantity  of  borax  should  be 
avoided,  as  this  gives  rise  to  a  very  hard  stony  slag  to  which  the 
lead  adheres  very  tenaciously.  On  hammering  such  a  slag  it  is 
liable  to  fly  to  pieces  with  explosive  violence,  carrying  with  it 
portions  of  the  lead.  There  is  also  a  possibility  that  some  gold 

i "  Metallurgy  of  Gold  on  the  Rand,"  1898. 

2"  Text  Book  of  Assaying,"  9th  edition,  p.  138. 

3  Ibid.,  p.  140. 


358  THE  CYANIDE  HANDBOOK 

and  silver  may  be  retained  chemically  in  slags  high  in  borax. 
With  little  or  no  borax  the  slag  is  usually  thick  and  not  very 
fusible. 

Excess  of  soda  gives  a  very  deliquescent  slag,  which  is  liable 
to  attack  the  crucibles. 

Excess  of  charcoal  gives  a  very  infusible  black  slag,  and  may 
cause  heavy  losses  in  gold  and  silver. 

The  use  of  salt,  sometimes  recommended  as  a  cover,  is  chiefly 
to  moderate  effervescence  during  the  expulsion  of  C02  in  the  early 
stages  of  the  fusion,  and  to  prevent  oxidation  of  lead  by  exposure 
to  air.  It  is  held  by  many  assayers  that  the  addition  of  salt 
causes  losses,  especially  of  silver,  hence  where  such  a  cover  is 
needed  it  is  better  to  use  borax.  The  writer  sometimes  uses  a 
cover  of  soda. 

Class  II.  —  Basic  Ores. 

The  general  principle  in  assaying  material  of  this  class  is  to 
increase  the  borax  and  reducing  agent,  and  to  somewhat  diminish 
the  alkaline  flux  (soda,  litharge).  Ferric  iron  should  be  con- 
verted as  much  as  possible  into  ferrous.  For  very  basic  ores  it 
is  advantageous  to  add  silica  or  other  acid  flux  in  addition  to 
borax. 

The  following  fluxes  are  suggested  for  assays  on  1  assay  ton 
of  ore: 

Flux.  No.  1  No.  2 

Carbonate  of  soda   18  30 

Borax 12  30 

Litharge 40  45 

Charcoal 2.5  2 

No.  1  is  adapted  from  a  flux  given  by  E.  A.  Smith,1  the  litharge 
and  charcoal  being  unchanged,  but  the  soda  and  borax  reduced 
proportionally  to  the  amount  of  ore  taken.  No.  2  is  given  by 
C.  and  J.  Beringer  (loc.  cit.,  p.  139). 

For  assays  on  2  assay  tons  of  ore: 

No.  1  No.  2  No.  3 

Carbonate  of  soda   90  36  12-18 

Borax 30  24                   36 

Litharge 45  40                   50 

Charcoal    -  2.5  4-6 

Sand  or  glass    -  12-24 

Argol      3 

i  "Assaying  of  Complex  Gold  Ores,"  in  Trans.  I.  M.  M.,  IX,  p.  320  (1901). 


SPECIAL  METHODS   OF  ASSAY  359 

Flux  No.  1  was  used  on  the  Rand  for  chlorination  tailings 
and  similar  material  that  was  mainly  siliceous,  but  contained 
some  ferric  oxide.  No.  2  is  adapted  from  a  flux  given  by  E.  A. 
Smith  (loc.  cit.),  the  soda  and  borax  being  increased  proportionally 
to  the  amount  of  ore,  leaving  the  litharge  and  charcoal  unchanged. 
No.  3  is  similarly  adapted  from  a  flux  given  by  Smith  for  very 
basic  ore. 

C.  and  J.  Beringer  (loc.  cit.,  p.  139)  also  give  the  following: 

No.  1  No.  2  No.  2a 

Charge  of  ore   2.5  assay  tons          50  grams  2  assay  tons 

Soda  (bicarbonate) ....    75  grams  30-50  grams  36-60  grams 

Soda  (carbonate) 50      "  20-33        "  24-40      " 

Borax 75       "  30          "  36         " 

Litharge 120      "  50          "  50         " 

Silica    -        "  10-25       "  12-30      " 

Charcoal    4       " 

Flour   -        "  7          "  7 

No.  1  is  for  low-grade  material  such  as  chlorination  tailings; 
to  be  assayed  in  a  large  crucible  (size  I) .  No  2  is  for  ore  consist- 
ing chiefly  of  hematite.  It  is  very  similar  to  the  flux  given 
by  Smith  for  very  basic  ore,  except  as  regards  the  amount  of 
soda. 

Some  assayers  use  metallic  iron  with  this  class  of  ore,  but  it 
would  seem  to  be  unnecessary  if  sufficient  reducing  agent  be  used. 
Finely  powdered  gas-carbon  has  been  recommended  as  a  very 
efficient  reducing  agent;  it  has  a  higher  reducing  power,  weight 
for  weight,  than  -charcoal,  and  being  less  rapidly  oxidized  acts 
for  a  longer  time  and  at  a  higher  temperature  during  the  course 
of  the  fusion. 

Class  III.  —  Pyritic  Ores 

Methods  of  Assaying  Pyritic  Ores.  —  The  principal  methods 
used  in  assaying  ores  containing  larger  or  smaller  amounts  of 
iron  pyrites  are: 

(a)  Roasting. 

(b)  Fusion  with  excess  of  litharge  and  little  or  no  reducing 
agent. 

(c)  Fusion  with  metallic  iron. 

(d)  Fusion  with  an  oxidizing  agent,  generally  niter. 
These  will  be  considered  in  the  order  given. 

(a)  Assay  by  roasting. —  According  to  the  richness  of  the  ore, 
1  or  2  assay  tons  are  weighed  out  and  placed  in  a  shallow  clay  dish 


360  THE  CYANIDE  HANDBOOK 

4  to  5  in.  in  diameter  and  spread  out  in  a  thin  layer.  Rectangular 
dishes  made  to  fit  inside  the  muffle  are  sometimes  used.  For 
highly  pyritic  ores  it  is  better  to  place  a  layer  of  silica  (15-20 
grams)  on  the  dish  before  adding  the  ore.  This  serves  to  prevent 
the  roasted  material  from  adhering  to  the  dish  and  also  aids  as 
a  flux  in  the  subsequent  fusion.  The  roasting-dish  is  placed 
at  the  mouth  of  a  large  muffle,  which  is  kept  for  some  time  at 
a  very  low  heat.  To  prevent  "  caking/'  or  the  formation  of  hard 
lumps  during  this  process,  the  contents  of  the  dish  are  stirred 
occasionally,  but  not  too  much,  with  a  thin  iron  rod,  bent  and 
flattened  at  the  end.  After  some  time,  if  much  pyrites  be  present, 
a  blue  flame  of  burning  sulphur  will  be  observed  over  the  dish. 
The  temperature  is  raised  gradually  to  dull  redness  and  the  dish, 
pushed  toward  the  back  of  the  muffle.  After  all  sulphur  fumes 
have  ceased  and  there  are  no  perceptible  sparks  on  stirring,  the 
temperature  may  be  further  raised  to  complete  the  roast.  The 
material  when  roasted  "  dead  "  should  have  a  uniform  appearance, 
and  should  emit  no  smell  whatever  of  sulphur,  etc.  Arsenical 
and  antimonial  ores  require  special  treatment  in  roasting,  which 
will  be  described  later.  When  the  roasting  is  complete,  the  dish 
and  contents  are  allowed  to  cool  (under  a  cover,  if  left  for  some 
time),  and  the  roasted  ore  swept  off  the  dish  into  a  mixture  of 
suitable  flux  by  means  of  a  small  flat  brush.  It  is  then  well 
mixed  with  the  flux  and  assayed  in  the  ordinary  way. 

When  roasted  without  silica,  the  ordinary  pyritic  ores,  con- 
sisting mainly  of  siliceous  materials  and  containing  not  more  than 
25-30  per  cent,  iron  pyrites,  may  be  assayed  by  one  of  the  first 
four  fluxes  given  for  basic  ores;  if  very  pyritic  (over  30  per  cent. 
FeS2)  the  flux  for  very  basic  ores  or  for  hematite  should  be  used 
for  the  roasted  material,  since  in  roasting  the  sulphides  of  iron 
are  converted  into  oxides.  The  process  takes  place  in  several 
stages,  but  the  ultimate  result  may  be  represented  thus: 

2FeS2  +  11O  =  Fe2O3  +  4SO2 

When  the  roasting  process  is  properly  carried  out,  the  heat 
kept  low  enough  in  the  early  stages  and  not  hurried,  and  when 
the  proper  flux  is  used  for  the  fusion  of  the  roasted  material,  the 
results  are  generally  at  least  as  good  as  those  obtained  by  any 
direct  fusion  method.  However,  the  time  occupied  in  the  roast- 
ing, often  an  hour  or  more,  is  a  disadvantage;  hence  the  method 


SPECIAL  METHODS   OF  ASSAY  361 

of  fusion  with  excess  of  litharge  is  to  be  preferred  for  slightly 
pyritic  material. 

Assay  of  Pyritic  Concentrates  by  Roasting.  —  The  method 
usually  adopted  by  the  writer  for  the  assay  of  pyritic  concentrates 
on  the  Rand  was  as  follows:  About  i  assay  ton  (say  15  grams)  of 
siliceous  sand,  free  from  gold  or  silver,  was  spread  out  on  a  5-in. 
roasting-dish,  and  1  assay  ton  of  the  concentrates  laid  in  a  thin 
layer  on  the  sand.  This  was  roasted  as  above  described,  and 
when  cool  mixed  thoroughly  with 

Carbonate  of  soda   90  grams 

Borax 30      " 

Litharge      50      " 

Gas  carbon    1.3       " 

and  fused.  The  carbon  was  varied,  if  necessary,  so  as  to  give  a 
button  of  18  to  25  grams. 

(b)  Fusion  with  Excess  of  Litharge.  —  The  principle  of  this 
method  is  that  lead  oxide  and  pyrites  act  on  one  another  when 
the  former  is  in  excess,  with  formation  of  oxides  of  iron  and  sul- 
phur, metallic  lead  being  liberated.  The  pyrites  thus  supplies 
the  place  of  the  whole  or  part  of  the  reducing  agent.  In  the  flux 
used,  rather  more  than  the  ordinary  amount  of  litharge  is  taken; 
the  charcoal  is  reduced  as  the  amount  of  pyrites  increases,  and 
in  some  cases  may  be  omitted  altogether. 

The  following  fluxes  maybe  used  for  an  ordinary  type  of  slightly 
pyritic  ore: 

No.  1  No.  2 

Ore  taken 1  assay  ton         2  assay  tons 

Carbonate  of  soda     45  grams  90  grams 

Borax 15      "  15      " 

Litharge 50      "  70      " 

Charcoal 0.8  to  nil   "        0.8  to  nil  " 

Mitchell  gives  the  following,  which  could  probably  be  used 
for  most  ores  of  this  class: 

Ore 1  assay  ton 

Carbonate  of  soda   30  grams 

Borax 30       " 

Litharge 150      " 

Salt  cover   30      " 

Argol,  sufficient  to  give  a  button  of  13  grams. 

[A  larger  button  would  probably  give  better  results. 

—  J.  E.  C.] 


362  THE  CYANIDE  HANDBOOK 

Limitations  of  the  Method.  —  The  method  is  not  convenient  for 
highly  pyritic  ores,  as  in  such  cases  a  large  amount  of  litharge 
must  be  added  to  ensure  having  an  excess,  and  consequently  very 
large  lead  buttons  are  produced,  which  must  be  reduced  subse- 
quently by  scorification.  If  the  litharge  be  not  in  excess,  the 
lead  button  will  be  brittle,  consisting  partly  of  lead  sulphide,  and 
more  or  less  of  the  values  will  be  lost. 

(c)  Fusion  with  Metallic  Iron.  —  The  principle  of  this  method 
is  to  convert  the  pyrites  into  ferrous  sulphide  in  accordance  with 
the  reaction:  FeSa  +  Fe  =  2FeS 


The  ferrous  sulphide  passes  into  the  slag  without  causing  any 
considerable  loss  of  precious  metal,  and  a  malleable  lead  button 
is  formed.  Large  nails  are  sometimes  used,  but  a  better  plan  is 
to  bend  a  piece  of  hoop-iron  in  U-shape;  this  is  pushed  into  the 
charge  in  the  crucible;  when  the  fusion  appears  to  be  complete 
and  the  slag  is  quite  fluid,  the  strip  of  iron  is  removed  with  the 
tongs,  tapped  once  or  twice  to  detach  any  adhering  slag  or  lead, 
removed  from  the  crucible,  and  the  fusion  continued  about  5 
minutes  longer  before  pouring. 

E.  A.  Smith1  gives  the  following  flux  as  suitable  with  this 
method  of  assay  (adapted  for  assay  of  2  assay  tons)  : 

Ore  ................................   2  assay  tons 

Carbonate  of  soda  ....................  48-60  grams 

Borax  ..............................  12-18      " 

Red  lead  ............................  48-60      " 

Charcoal  ............................  2  to  nil 

Hoop-iron  (thick)  ..........  2  or  3  pieces  to  be  added 

Aaron2  gives  the  following: 

Ore     ..............    1  assay  ton 

Carbonate  of  soda    .  .  90  grams 
Borax  .............  15       " 

Litharge      .........  30       " 

Sulphur...  .........   3       " 

Flour   .............   3       " 

Iron  nails      ........   3  to  be  added  (with  glass,  if  a  more  acid  flux  is  needed, 

and  a  cover  of  salt). 
[The  object  of  the  sulphur  is  not  particularly  obvious.  —  J.  E.  C.] 

This  method  requires  considerable   care  and  experience  for 

i  "  Assaying  of  Complex  Gold,  Ores,"  in  Trans.  I.  M.  M.,  IX,  p.  320. 
a  Rose,  "  Metallurgy  of  Gold,"  4th  edition,  p.  469. 


SPECIAL  METHODS   OF  ASSAY  363 

satisfactory  results.  The  strips  of  iron  when  withdrawn  from 
the  crucibles  are  apt  to  carry  small  adhering  shots  of  lead,  and 
should  be  carefully  examined. 

(d)  Assay  with  Niter.  —  In  this  method  it  is  presupposed  that 
the  quantity  of  pyrites  in  the  ore  is  more  than  sufficient  to  bring 
down  the  required  amount  of  lead.  The  surplus  lead  is  oxidized 
by  the  addition  to  the  flux  of  a  carefully  adjusted  quantity  of 
niter.  [It  is  more  probable  that  the  niter  attacks  the  iron  pyrites 
rather  than  the  lead,  as  the  slag  in  this  process  invariably  con- 
tains potassium  sulphate.]  An  excess  of  niter  causes  heavy  losses 
of  precious  metals,  and  sometimes  causes  corrosion  of  the  crucible 
itself;  hence  when  this  method  is  tried  on  an  unknown  ore,  a  trial 
fusion  is  always  made  to  determine  the  "  reducing  power  "  of  the 
ore.  In  such  a  case,  some  such  mixture  as  the  following  is  made: 

Ore     i  assay  ton  (7.292  grams) 

Litharge      60  grams 

Carbonate  of  soda   4       " 

Miller,  Hall,  and  Falk1  give  the  following: 

Ore 3  grams 

Soda  bicarbonate 10      " 

Litharge 50      " 

Salt  cover 

The  mixture  is  fused  at  a  bright  red  heat  for  from  10  to  15 
minutes,  then  poured,  and  the  resulting  lead  button  weighed.  The 
weight  of  this  button  is  a  measure  of  the  reducing  power  of  the 
ore.  It  is  generally  assumed  that  1  gram  of  niter  will  oxidize  4 
grams  of  lead.  E.  A.  Smith  (loc.  cit.,  p.  335)  says  4  to  5  grams, 
but  the  amount  varies  with  the  nature  of  the  ore,  and  may  range 
from  3.2  to  5.3. 

Formula  for  Niter  Required.  —  The  following  is  a  general 
formula  which  can  be  applied  in  all  cases  for  calculating  the  amount 
of  niter  required: 

Let    a  =  weight  of  ore  taken  for  trial  fusion. 
'     A  =  weight  of  ore  taken  for  final  assay. 
<     w  =  weight  of  lead  button  from  trial  fusion. 
'    W=  weight  of  lead  button  required. 

'     n  =  number  of  grams  lead  oxidized  by  one  gram  of  niter. 
'     x  =  weight  of  niter  required. 
Then 

Aw  — Wa 

x  = 

na 

i  Trans.  A.  I.  M.  E.,  XXXIV,  p.  387. 


364 


THE  CYANIDE  HANDBOOK 


In  the  special  case  where  1  gram  niter  oxidizes  4  grams- lead, 
and  J  assay  ton  is  taken  for  trial  fusion,  1  assay  ton  for  final 
fusion,  and  a  button  of  20  grams  is  required,  we  have 

x  =  w  —  5 

Oxidizing  Power  of  Niter  on  Various  Minerals.  —  Smith  (loc. 
cit.,  p.  327)  gives  the  following  table  to  determine  the  oxidizing 
effect  of  niter,  when  the  nature  and  amount  of  the  oxidizable 
material  is  known: 

TABLE  VI.  —  OXIDIZING  EFFECT  OF  NITER 


Parts  Niter  Required  to  1  Part  of  "  Sulphuret  " 

Iron  pyrites  

2-2  £  parts 

Copper  pyrite,  fahlerz,  or  zinc-blende 
Antiinonite  . 

li-2     " 
U       " 

Galena  

*       " 

No.  2 

|  assay  ton 
15  grams 

15      " 
_        « 

70       " 


Final  Fusion.  —  For  the  final  fusion,  as  a  rule,  a  flux  is  used 
containing  much  litharge  and  little  soda,  together  with  the  indi- 
cated amount  of  niter  and  a  cover  of  salt  to  modify  the  effer- 
vescence. The  violent  action  is  a  frequent  cause  of  loss  in  assays 
with  niter.  The  following  may  be  given  as  examples  of  fluxes 
for  the  final  fusion : 

No.  1 

Ore 2  assay  tons 

Bicarbonate  of  soda  ...       45  grams 

Carbonate  of  soda 30      " 

Borax 12       " 

Litharge      — 

Red  lead   120      " 

Niter  as  indicated. 
Salt  cover. 

No.  1  is  given  by  E.  A.  Smith  (loc.  cit.).  No.  2  is  given  by 
Miller,  Hall,  and  Falk  (loc.  cit.).  These  authors  found  that  the 
use  of  borax  was  objectionable,  giving  an  excessively  hard  and 
stony  slag,  with  hard  brittle  lead  buttons.  [This  would  probably 
apply  only  to  certain  classes  of  ore.  —  J.  E.  C.]  They  summarized 
their  experience  of  the  process  as  follows: 

"  It  is  necessary  to  determine  the  oxidizing  power  of  niter  with 
that  substance  and  charge  with  which  it  is  subsequently  used; 
the  niter  method,  as  modified,  gives  accurate  results  and  is  neither 
as  long  nor  as  tedious  as  the  roasting  method;  it  also  gives  a 


SPECIAL  METHODS  OF  ASSAY  365 

charge  which  does  not  boil  over,  and  yields  a  lead  button  agree- 
ing closely  with  the  calculated  weight,  and  a  clean  slag." 

Another  method  of  applying  niter  in  assaying  will  be  described 
under  "Antimonial  Ores"  (Class  VI). 

Class  IV.  —  Lead-Zinc  Ores 

Ores  containing  galena  and  zinc-blende  are  best  assayed  by 
fusion  with  metallic  iron,  as  already  described  under  "Pyritic 
Ores"  (Class  III,  c).  Where  galena  predominates,  the  amount  of 
litharge  may  be  reduced;  when  the  zinc  mineral  predominates, 
the  amount  of  soda  and  borax  should  be  increased.  One  of  the 
two  fluxes  given  above  will  probably  meet  most  cases. 

Hall  and  Popper1  give  the  following  as  suitable  to  certain 
kinds  of  zinc  ore  (sphalerite) : 

Ore     i  assay  ton,  say  10  grams 

Carbonate  of  soda       1J      "  "40      " 

Borax  glass     i      "  "15      " 

Litharge      |      "  "24       " 

Argol  as  required. 

Add  iron  if  more  than  15  per  cent,  pyrites  is  present.  [The 
amount  of  soda  here  seems  excessive,  and  in  fact  the  authors 
remark  that  the  silica  of  the  crucible  appeared  to  be  attacked, 
and  the  charge  was  inclined  to  boil  excessively.  —  J.  E.  C.] 

Roasting  may  be  employed  when  the  ore  is  chiefly  or  exclusively 
zinc-blende,  but  is  unsatisfactory  with  any  but  very  small  quan- 
tities of  galena. 

Class  V.  —  Arsenical  Ores 

Mode  of  Occurrence.  —  The  arsenic  in  gold  ores  usually  occurs 
as  mispickel  (FeAsS),  occasionally  as  arsenide  of  nickel  or  as 
realgar  and  orpiment  (sulphides  of  arsenic). 

Roasting  with  Charcoal.  —  The  best  method  is  to  first  roast  at 
a  low  temperature,  eliminating  part  of  the  arsenic,  then  allow  to 
cool  somewhat;  add  5  to  10  per  cent,  of  powdered  charcoal,  stirring 
well,  to  mix  with  the  charge  on  the  roasting-dish,  and  continue 
heating  at  a  somewhat  higher  temperature  until  a  dead  roast  is 
obtained.  The  roasted  material  is  then  fluxed  as  described  under 
basic  ores,  or  pyritic  ores  after  roasting. 

i "  Sch.  Mines  Quart.,"  XXV,  p.  355  (1904). 


366  THE  CYANIDE  HANDBOOK 

Theory  of  Method.  —  The  object  of  adding  charcoal  is  to  de- 
compose the  arseniates  formed  in  the  first  stage  of  roasting.  These 
compounds,  if  not  destroyed,  would  carry  gold  and  silver  into  the 
slag.  It  has  been  stated1  that  the  addition  of  a  small  quantity 
of  potassium  cyanide  to  the  flux  facilitates  the  decomposition  of 
any  arseniates  remaining  in  the  roasted  product.  It  is  not 
advisable  to  assay  ores  of  this  class  by  means  of  niter,  as  this 
tends  to  form  arseniates. 

Class  VI.  —  Antimonial  Ores 

Various  Methods  for  Antimonial  Ores.  —  The  methods  usually 
adopted  for  assaying  ores  of  this  class  may  be  divided  as  follows: 

(a)  Fusion  with  niter. 

(6)  Preliminary  oxidation  with  niter  or  other  oxidizer,  fol- 
lowed by  fusion  with  a  reducing  flux. 

(c)  Preliminary  acid  treatment,  to  eliminate  as  much  as  pos- 
sible of  the  antimony,  followed  by  scorification  or  fusion  of  the 
residue. 

(a)  Fusion  with  Niter.  —  The  details  of  this  method  have 
already  been  given  under  "Pyritic  Ores"  (Class  III,  d).  E.  A. 
Smith  (toe.  cit.,  p.  334)  gives  the  following  flux  for  an  ore  containing 
75  per  cent,  of  stibnite  (here  adapted  for  assay  on  2  assay  tons) : 

Ore     2  assay  tons 

Carbonate  of  soda    50  grams 

Borax 12       " 

Red  lead   120       " 

Niter 36-48  " 

Salt  cover. 

A  large  crucible  must  be  used,  raising  the  temperature  very 
gradually  at  first.  The  slag  is  very  fluid.  "  When  effervescence 
has  ceased  and  the  contents  of  the  crucible  have  become  thoroughly 
liquid  and  tranquil,  it  is  advisable  to  lift  the  crucible  out  of  the 
fire  and  subject  it  to  a  rotary  motion,  in  order  to  thoroughly  mix 
the  liquid  contents.  If  this  causes  effervescence  it  indicates  that 
the  action  of  the  niter  is  not  complete,  and  the  crucible  must  be 
returned  to  the  fire  and  the  fusion  continued  "  (Smith) . 

(6)  Preliminary  Oxidation  with  Niter.  —  This  method  requires 
some  previous  knowledge  of  the  nature  of  the  ore.  The  charge 
of  ore  is  placed  in  a  crucible  with  niter  equal  to  twice  the  weight 

*  E.  A.  Smith,  Ibid.,  p.  332, 


SPECIAL  METHODS  OF  ASSAY  367 

of  the  pyritic  material  contained  in  the  ore,  together  with  soda 
and  borax,  say  for  2  assay  tons  of  ore:  soda  50  grams,  borax 
10  to  15  grams,  niter  (as  required)  up  to  80  or  90  grams.  When 
the  action  appears  to  be  complete  and  the  fusion  is  tranquil,  the 
crucible  is  withdrawn  from  the  fire  and  allowed  to  cool  until  the 
slag  begins  to  thicken.  The  following  mixture  is  then  added, 
and  fused  for  10  to  15  minutes: 

Borax      10  grams 

Red  lead   40      " 

Charcoal    2      " 

Several  variations  of  this  method  have  been  used,  and  a  some- 
what similar  method  has  been  proposed  by  K.  Sander  for  assaying 
carbonaceous  matter  containing  lead,  in  which  the  preliminary 
oxidation  is  made  with  a  mixture  of  niter  and  sodium  peroxide. 
(See  below.) 

(c)  Preliminary  Acid  Treatment.  —  The  following  combined 
wet  and  dry  method  depends  on  the  fact  that  sulphide  of  antimony 
is  soluble  in  strong  hydrochloric  acid.  The  native  oxides  are, 
however,  only  partially  soluble.  "The  weighed  quantity  of  ore 
(30  to  50  grams)  is  treated  with  concentrated  hydrochloric  acid 
and  heated  until  decomposition  is  complete;  the  solution  is  diluted 
with  a  small  quantity  of  water  containing  a  little  tartaric  acid  to 
prevent  precipitation  of  antimony  as  oxychloride.  The  insoluble 
residue  is  allowed  to  settle,  and  when  the  solution  is  clear  as  much 
of  the  liquid  as  possible  is  poured  off  through  a  filter,  without 
disturbing  the  residue.  The  latter  is  finally  transferred  to  the 
filter,  allowed  to  drain,  and  dried.  The  filter-paper  is  burnt,  and 
the  ash,  with  the  insoluble  residue,  is  scorified  with  ten  times  its 
weight  of  grain-lead  and  a  borax  cover,  or  fused  with  the  follow- 
ing flux:"  E.  A.  Smith  (loc.  cit.). 

Soda  carbonate  and  borax  together 30  grams 

Red  lead   30       " 

Charcoal    1.5      " 

Class  VII.  —  Cupriferous  Ores 

Methods  of  Assaying.  —  The  methods  usually  applied  for  this 
class  of  ore  are: 

(a)  Preliminary  acid  treatment  to  remove  the  bulk  of  the 
copper,  followed  by  fusion  or  scorification  of  the  residue. 


368  THE  CYANIDE  HANDBOOK 

(b)  Fusion  with  a  large  excess  of  lead  oxide,  using  charcoal 
or  niter  according  to  the  nature  of  the  ore. 

(a)  Assay  with  Preliminary  Acid  Treatment.  —  Dr.  J.  Percy1 
gives  the  following  method  (grains  are  here  expressed  in  the  nearest 
equivalent  in  grams) : 

"Six  or  seven  grams  of  ore  are  heated  with  nitric  acid,  or  a 
mixture  of  nitric  and  sulphuric  acids.  The  liquid  is  then  diluted, 
a  little  hydrochloric  acid  or  salt  added  to  precipitate  silver,  after 
which  the  solution  is  filtered.  The  filtrate  is  clear;  contains  most 
of  the  copper,  and  may  be  rejected.  The  residue  is  dried  and 
fused  with 

Soda  and  borax 20  grams 

Red  lead    20       " 

Charcoal    1       " 

for  10  to  15  minutes." 

In  a  modification  of  this  method  given  by  E.  A.  Smith  (loc. 
cit.) ,  30  to  50  grams  of  the  ore  are  treated  with  fuming  nitric  acid 
till  decomposed,  heated  to  expel  nitrous  acid,  then  diluted  and 
mixed  with  a  little  HC1  or  salt  to  precipitate  silver.  The  ore  is 
then  stirred,  settled,  and  decanted  through  a  filter.  The  dried 
residue,  with  the  filter-paper,  is  fluxed  with 

Soda  and  borax  (together) 30  grams 

Red  lead    30       " 

Charcoal    1.5      " 

or  it  may  be  scorified  with  ten  times  its  weight  of  lead. 

The  writer's  experience  of  this  method  is  that  the  filtration 
is  very  tedious  unless  a  long  time  be  allowed  for  settlement,  as 
with  most  ores  a  considerable  portion  is  crushed  fine  enough  to 
produce  slimes,  which  soon  choke  the  filter.  Moreover,  the  method 
for  precipitating  the  silver  is  certainly  faulty,  for  if  insufficient 
HC1  or  salt  be  added,  the  silver  will  not  be  completely  precipi- 
tated, whereas  an  excess  of  either,  together  with  the  nitric  acid 
present,  would  dissolve  gold.  A  better  plan  would  be  to  filter 
without  addition  of  chlorides  and  precipitate  or  titrate  the  silver 
separately  in  the  filtrate;  or  make  an  entirely  independent  assay 
of  it  by  scorification  or  some  other  method. 

A  similar  method,  due  to  C.  Whitehead,2  in  which  the  silver 

1  "  Metallurgy:  Silver  and  Gold,"  Part  I,  p.  115. 

2  See  R.  W.  Lodge  in  Trans.  A.  I.  M.  E.,  XXXIV,  p.  432. 


SPECIAL   METHODS   OF   ASSAY 


369 


in  the  filtrate  is  precipitated  by  potassium  bromide,  was  found  by 
Lodge  to  give  low  results. 

(b)  Direct  Fusion  with  Excess  of  Litharge.  —  In  all  cases  where 
cupriferous  ores  are  fused  without  preliminary  acid  treatment, 
a  large  quantity  of  lead  oxide  must  be  used,  and  the  resulting 
large  lead  button  reduced  by  scorification  before  cupeling.  When 
the  buttons  are  hard  and  have  a  coppery  appearance,  they  should 
be  still  further  scorified,  with  addition  of  more  lead.  According 
to  Percy  (loc.  cit.)  one  part  by  weight  of  copper  requires  about 
16  parts  of  lead  for  cupellation,  and  although  a  smaller  quantity 
of  lead  will  pass  the  copper  into  the  cupel,  yet  in  that  case  some 
considerable  amount  of  gold  and  silver  is  also  absorbed  by  the 
cupel. 

The  three  following  fluxes  (adapted  from  Percy)  are  given  by 
E.  A.  Smith  (loc.  cit.)  for  ores  containing  various  amounts  of 
copper  (the  weights  in  grams) : 


No.  1 

No.  2 

No.  3 

Ore  

10-50 

10-50 

1  assay  ton 

Soda  Carbonate            .... 

20-30 

120 

Borax 

15-20 

Silica    

10-25 

Red  lead 

200-300 

100 

150 

Charcoal  

1  5-3.5 

3.5 

Niter 

18 

No.  1  is  for  ores  containing  only  moderate  amounts  of  copper; 
No.  2  for  ores  after  roasting,  No.  3  for  gray  antimonial-copper  ore 
containing  say  30  per  cent.  Cu  and  150  oz.  Ag  per  ton. 

The  quantities  of  charcoal  and  niter  would  of  course  be  varied 
according  to  circumstances. 


Class  VIII.  —  Telluride  Ores. 

Points  to  be  Observed  in  Assaying  Telluride  Ores.  —  An  excel- 
lent article  on  the  assaying  of  gold  telluride  ores,  by  W.  F.  Hille- 
brand  and  E.  T.  Allen,  will  be  found  in  Bulletin  No.  253  of  the 
United  States  Geological  Survey  (1905).  The  essential  points 
in  assaying  these  ores  appear  to  be:  (a)  Very  fine  grinding  of 
the  sample,  say  to  150-  or  200-mesh;  (b)  considerable  excess  of  lead 


370  THE  CYANIDE  HANDBOOK 

oxide;  (c)  avoidance  of  roasting,  scorification,  or  any  oxidation 
process,  either  for  the  ore  or  the  lead  buttons;  hence  the  button 
produced  should  not  be  larger  than  can  be  cupeled  direct. 

Flux  for  Cripple  Creek  Tellurides.  —  Hillebrand  and  Allen 
found  the  following  flux  to  give  very  satisfactory  results  on 
Cripple  Creek  telluride  ores,  using  a  Battersea  "  F "  crucible  for 
the  fusion: 

Ore 1  assay  ton 

Bicarbonate  of  soda 30  grams 

Carbonate  of  soda 20 

Fused  borax 10      " 

Litharge 120-180  grams 

Salt  cover. 

This  gave  lead  buttons  of  about  25  grams  weight,  without 
addition  of  iron  or  niter.  The  losses  in  the  slag  were  very  slight; 
those  by  absorption  in  the  cupels  were  more  considerable  and 
were  corrected  by  a  subsequent  assay  of  the  cupels. 

Precautions.  —  With  ores  of  this  class  great  care  is  necessary 
in  moderating  the  heat  in  the  early  stages  of  the  fusion,  and  with 
an  ore  not  previously  tested  it  would  always  be  as  well  to  remelt 
the  slag  with  fresh  flux.  In  the  case  of  rich  tellurides  it  is  better 
to  reduce  the  charge  of  ore  rather  than  increase  the  litharge,  so 
as  to  avoid  producing  an  unduly  large  lead  button.  The  losses 
in  oxidizing  telluride  ores  or  lead  buttons  containing  tellurium 
appear  to  be  due  to  the  volatilization  of  tellurium  trioxide,  which 
carries  off  gold  mechanically.  Smith  (loc.  cit.,  p.  344)  states  that 
in  presence  of  lead  oxide  tellurium  is  readily  converted  into  telluric 
acid,  which  combines  with  the  lead  oxide  when  the  latter  is  in 
excess:  Te  +  4pbo  =  3pb  +  PbTeO4 

but  if  the  contrary  be  the  case,  the  excess  of  telluric  acid  is  volatil- 
ized and  telluride  of  lead  is  produced: 

2Te  +  3PbO  =  TePb3  +  TeO3. 

Fluxes  for  Telluride  Ores.  —  Smith  gives  the  following  fluxes 
(adapted) : 


u/. 
Ore  . 

No.  1 
(for  ordinary  assay) 

2  assay  tons 

No.  2 
(for  very  rich  ores) 

4-  assay  ton 

Carbonate  of  soda    . 
Borax  . 

60  grams 
24       " 

50  grams 

u 

Siliceous  sand 
Red  lead    
Charcoal    

.    12-36       " 
.50-200       " 
1-2       " 

5-10      " 
100-150      " 
1       " 

Salt  cover. 

SPECIAL  METHODS   OF  ASSAY  371 

The  red  lead  is  varied  according  to  the  tellurium  present,  and 
charcoal  according  to  the  reducing  power  of  the  ore.  The  char- 
coal may  be  omitted  in  some  cases. 

Combined  Wet  and  Dry  Assay.  —  The  following  method  is 
given  by  Hillebrand  and  Allen  (loc.  cit.).  "Fifty-gram  portions 
were  mixed  with  water  in  large  porcelain  basins,  and  strong 
nitric  acid  was  added  by  degrees,  with  constant  stirring,  till  the 
action  had  nearly  ceased;  then  bromine  water  was  added  to 
oxidize  the  gold  and  sulphur  and  precipitate  the  silver,  no  arti- 
ficial heat  being  used."  After  thorough  settling,  the  residue 
was  filtered  and  washed  repeatedly  with  water  containing  Br 
and  HC1,  and  then  washed  two  or  three  times  with  pure  water. 
The  combined  filtrates  were  evaporated  in  the  original  basins 
to  near  dryness,  then  treated  with  HC1  and  covered  for  a  time. 
When  action  ceased  the  covers  were  removed  and  evaporation 
continued,  HC1  being  added  two  or  three  times  more  at  intervals. 
The  residues  were  now  digested  with  dilute  HC1  and  a  little 
bromine  water  to  insure  solution  of  the  gold.  Considerable  calcium 
sulphate  remained  undissolved,  which  was  filtered  off  and  found 
to  be  practically  free  from  gold.  The  filtrate  was  precipitated 
with  ferrous  sulphate,  allowed  to  stand  for  24  hours,  and  the 
precipitated  gold  collected  on  a  filter,  washed,  dried,  weighed, 
cupeled,  and  again  weighed  (using  a  check  of  proof  gold  for  cor- 
rection). The  gold  thus  thrown  down  was  found  to  be  free  from 
tellurium. 

The  residue,  containing  the  silver  and  a  small  quantity  of 
gold  not  extracted  by  the  washing,  was  dried  and  assayed  with 
the  following  flux,  yielding  a  lead  button  of  20  grams: 

Carbonate  of  soda   30  grams 

Borax 10      " 

Litharge 60      " 

Argol   2      " 

Salt  cover. 

(C)  ASSAY  OF  CERTAIN  REFRACTORY  MATERIALS 

Among  the  products  which  the  cyanide  chemist  may  occa- 
sionally be  called  upon  to  assay  may  be  mentioned  zinc-gold 
precipitate  (with  or  without  roasting  or  acid  treatment),  slags 
from  fusion  of  zinc  precipitate,  etc.,  slags  and  cupels  from  the 
assay  of  different  classes  of  ore  (when  exact  results  are  required 


372  THE  CYANIDE  HANDBOOK 

on  rich  material),  old  crucibles,  cupel  and  furnace  bottoms,  bat- 
tery screening,  scalings  from  plates,  prussian  blue,  ferric  hydrate 
and  other  deposits  from  tanks  or  precipitation  boxes,  residues 
from  smelting  retorts,  sweep  from  smelting  room,  old  sacking  and 
filter-cloths,  and  other  matters  of  very  varied  description.  Of 
course,  no  general  rule  can  be  given  for  the  treatment  of  such 
material,  but  a  few  remarks  may  be  of  use: 

Where  the  material  does  not  admit  of  fine  subdivision  no  reli- 
able assay  can  be  made,  unless  a  very  large  sample  be  taken  and 
the  whole  of  it  weighed  and  subjected  to  some  process  for  redu- 
cing the  bulk  without  loss  of  values.  Thus,  samples  consisting 
largely  of  metal  may  often  be  treated  by  dissolving  in  some  suitable 
acid,  depending  on  the  nature  of  the  material;  an  assay  is  then 
made  by  scorification  or  otherwise  on  the  dried  residue  insoluble 
in  that  acid;  the  residue,  after  acid  treatment,  is  of  course  weighed 
again,  unless  the  whole  of  it  can  be  dealt  with  in  one  operation  for 
extraction  of  its  values.  In  other  cases,  where  a  large  part  of  the 
sample  is  inflammable,  the  whole  may  be  weighed,  and  then  roasted 
or  burnt  with  suitable  precautions  and  an  assay  made  on  the  ash. 

Samples  Containing  Metallics.  —  Material  of  this  class  fre- 
quently contains  metallic  particles,  such  as  shots  or  flakes  of  bullion, 
of  totally  different  and  usually  much  higher  assay  value  than  the 
remainder.  In  all  such  cases  the  entire  sample  should  be  first 
weighed.  It  is  then  crushed,  and  as  much  as  possible  passed  through 
a  sufficiently  fine  sieve.  The  portion  which  passes  the  sieve,  and 
the  metallic  and  other  particles  remaining  on  the  sieve,  are  then 
weighed  and  assayed  separately. 

Formula  for  Assays  with  Metallics.  —  The  following  formula 
may  be  used  in  the  ordinary  case,  where  the  whole  of  the  metallic 
portion  is  treated  to  recover  its  entire  gold  or  silver  contents,  and 
an  assay  made  in  the  usual  way  on  the  fine  portion. 

Let  M  =  total  weight  of  metallics  in  grams. 
F   =  total  weight  of  fines  in  grams. 
m  =  weight  in  mg.  of  the  metal  sought  (gold  or  silver)  contained 

inM. 

a  =  assay  of  metallics  (in  dwt.  per  ton  of  2000  Ib.) 
b  =  assay  of  fines  (in  dwt.  per  ton  of  2000  Ib.) 
x  =  assay  of  entire  sample  (in  dwt.  per  ton  of  2000  Ib.) 

12  Fb  +  7000m 


12  (M  +  F)  M  +  F 


SPECIAL  METHODS   OF   ASSAY  373 

In  the  case  where  an  assay  is  made, on  a  part  only  of  each 
product,  ^  Ma  +  Fb 

Some  of  the  substances  above  mentioned  are  similar  in  com- 
position to  one  or  other  of  the  classes  of  ore  previously  discussed, 
and  may  be  assayed  by  the  methods  of  crucible  fusion  already 
given,  but  scorification  is  more  generally  applicable. 

Assay  of  Slags.  —  Slags  (from  melting  of  zinc-gold  precipitate, 
etc.)  usually  require  a  considerable  amount  of  litharge  and  re- 
ducer, so  as  to  give  a  large  lead  button.  Occasionally  they  are 
mixed  with  so  much  carbonaceous  matter  that  niter  must  be 
used  instead  of  reducing  agent.  Roasting  cannot  be  used  for 
this  class  of  material,  as  it  would  fuse  and  attack  the  silica  of  the 
dish,  forming  a  crust  which  would  not  afterwards  be  separated 
without  loss. 

Slags  from  Assay  Fusions  frequently  have  to  be  remelted  with 
fresh  flux  to  recover  the  values  passing  into  them  in  the  first 
fusion.  It  is  usually  sufficient  to  powder  the  slag  coarsely  and 
return  it  to  the  original  crucible,  together  with  about  50  grams 
of  the  ordinary  assay  flux.  This  is  fused  for  10  to  15  minutes, 
and  the  small  resulting  lead  button  cupeled  with  the  original 
button,  or  preferably  on  a  separate  cupel,  so  that  the  amount 
recovered  from  the  slag  may  be  noted.  The  following  fluxes  may 
be  mentioned,  given  by  different  authorities  as  suitable  for  re- 
melting  the  assay  slags  from  various  kinds  of  material: 

No.  1.     E.  A.  Smith  (loc.  cit.,  p.  322): 

Soda  carbonate 10  grams 

Litharge 30       " 

Charcoal    1.5        " 

Borax  added  if  mixture  does  not  fuse  quickly. 

No.  2.     Adapted  from  Percy,  loc.  cit.  (fuse  for  15  to  20  minutes) 

Soda  carbonate 2-3.5  grams 

Red  lead   20-33 

Charcoal    1-2         " 

No.  3.  For  rich  silver-lead  ore  —  cerussite  (Miller  and  Ful- 
ton1). Slag  is  first  remelted  with  litharge,  1  assay  ton,  argol, 
2  grams,  and  then  the  large  lead  button  resulting  is  scorified.  The 
slag  from  this  scorification  is  further  run  down  with 

i"  Sch.  Mines  Quart.,"  XVII,  p.  160. 


374  THE  CYANIDE  HANDBOOK 

Carbonate  of  soda   1  assay  ton 

Silica    £     " 

Litharge 1      "       " 

Argol    2  grams 

No.  4.  For  remelting  slags  from  assay  of  telluride  ores  (Hille- 
brand  and  Allen,  loc.  cit.) : 

Litharge 1  assay  ton 

Argol 2  grams 

Salt  cover. 

Assay  of  Bone-ash  Cupels. —  It  is  usually  only  necessary  to  test 
the  portion  of  the  cupel  which  has  been  stained  by  absorbed 
litharge.  The  remainder  is  scraped  off  and  rejected,  and  the 
portion  for  assay  finely  powdered  (at  least  to  80-mesh).  T.  Kirke 
Rose1  gives  the  following  as  a  suitable  flux: 

Ground  cupels    100  parts 

Carbonate  of  soda    100      " 

Borax 50      " 

Sand 75      " 

Fluor-spar 75      " 

Litharge 50      " 

Charcoal    4      " 

Percy  (loc.  cit.)  gives: 

Carbonate  of  soda    7-17  grams 

Borax 7-17       " 

Fluor-spar 7-17       " 

Charcoal,  4  to  5  parts  for  every  part  of  litharge  in  the  cupel ;  if  the  latter 
is  insufficient,  add  red  lead,  20  grams,  charcoal,  1  gram. 
Instead  of  borax,  glass  free  from  lead  may  be  used. 

The  two  following  fluxes  also  are  given  by  (1)  Hillebrand  and 
Allen,  and  (2)  Miller  and  Fulton: 

No.  1  No.  2 

Carbonate  of  soda    30  grams  30  grams 

Borax 45       "  30       " 

Litharge 60       "  60       " 

Argol    2       "  2       " 

Cover  of  salt. 

For  cupels  which  have  been  used  in  the  assay  of  zinc-gold 
precipitate  the  following  are  given  by  (1)  R.  W.  Lodge  (Trans. 
A.  I.  M.  E.,  XXXIV,  p.  432),  and  (2)  W.  Magenau  ("Min.  and 
Sci.  Press,"  LXXX,  p.  464).  The  quantities  are  given  in  grams: 

i  ".Metallurgy  of  Gold,"  4th  edition,  p.  481. 


SPECIAL  METHODS   OF  ASSAY  375 

No.  1  No.  2 

Cupels   30-40 

Carbonate  of  soda   15  40 

Borax 10  10 

Silica    -  10 

Glass    15 

Litharge 60  20 

Argol   2 

Flour   -  1 

Cover  of -  borax 

Graphite  Crucibles.  —  A  method  for  assaying  graphite  cru- 
cibles by  scorification  has  already  been  given  in  Section  III. 
The  following  methods  of  crucible  fusion  may  here  be  noted. 

R.  Dures,1  after  sifting  out  all  shots,  etc.,  from  the  finely- 
ground  material,  fluxes  the  remainder  thus: 

Finely  ground  crucible 5  grams 

Carbonate  of  soda   25       " 

Borax 15       " 

Silica    10      " 

Litharge 85       " 

Niter    7       " 

A.  F.  Crosse2  gives  a  method  of  assaying  this  material  by 
preliminary  oxidation  with  manganese  peroxide,  taking 

Powdered  crucibles 10  grams 

Manganese  dioxide 35      " 

After  heating  this  mixture  to  bright  redness  in  an  "  H  "  cru- 
cible, the  temperature  is  reduced,  and  the  following  flux  added : 

Potassium  carbonate 50  grams 

Borax 25       " 

Salt 25       " 

Litharge 50       " 

Silica    20      " 

Flour 2       " 

In  some  cases  the  manganese  dioxide  may  be  omitted  and  the 
material  given  a  preliminary  roast  with  silica,  using 

Powdered  crucibles   : 1  assay  ton 

Quartz 2  assay  tons 

Other  assayers,  however,  obtained  very  low  results  by  Crosse's 
method,  and  Dr.  J.  Loevy3  recommends  scorifying 

1 "  Journ.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  p.  577. 
»"  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  p.  124. 
•  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  p.  205. 


376  THE  CYANIDE  HANDBOOK 

Powdered  crucibles    5  grams 

(Lead 60       " 

I  or  Litharge 70       " 

with  a  small  quantity  of  borax  or  glass. 

Battery  Scrapings  (and  other  coppery  material  of  similar 
nature).  —  R.  Dures  (loc.  cit.}  prefers  scorification  to  nitric  acid 
treatment  for  this  class  of  material,  on  the  ground  that  the  nitrous 
acid  always  present  in  the  commercial  acid  causes  loss  of  gold. 
(See  Section  II,  b.)  Williams  and  Crosse,  however,  advocate  acid 
treatment,  and  the  latter  adds  lead  acetate  and  sulphuric  acid 
to  form  a  precipitate  of  lead  sulphate,  which  helps  to  carry  down 
the  gold. 

Zinc-Box  Precipitate.  —  No.  1.  The  following  scorification 
charge  is  given  by  R.  W.  Lodge l : 

Precipitate     0.05  assay  ton 

Grain  lead   65  grams 

Borax  glass 10       " 

Of  the  65  grams  of  lead,  35  grams  are  to  be  mixed  with  the 
charge  and  the  remaining  30  grams  are  to  be  used  as  a  cover. 
Use  a  3-in.  to  4-in.  scorifier.  The  slag  from  this  to  be  remelted 

with 

Soda  carbonate 15  grams 

Glass    10       " 

Litharge 30       " 

Argol 2       " 

and  the  cupels  assayed  as  described  above. 

No.  2.     C.  H.  Fulton  and  C.  H.  Crawford  2  give  the  following: 

Precipitate 0.05  assay  ton 

Grain  lead 70  grams 

Litharge 15       "      )     ,  ,    , 

-n  t       it      t  added  as  cover 

Borax 1  ) 

But  these  writers  prefer  a  "wet  and  dry"  method,  as  follows: 
No.  3.  One-tenth  assay  ton  of  the  precipitate  is  boiled  with 
a  mixture  of  20  c.c.  cone.  H2SO4  and  60  c.c.  water;  then  75  cc. 
normal  NaCl  and  20  c.c.  lead  acetate  solution  (strength  not  given) 
are  added.  The  precipitate  is  settled  for  an  hour,  filtered,  washed, 
and  dried,  care  being  taken  to  wash  into  the  point  of  the  filter. 
The  paper  is  then  burnt  at  a  low  heat  and  the  whole  residue 

i  Trans.  A.  I.  M.  E  ,  XXXIV,  p.  432  (October,  1903). 
a"  Sch.  Mines  Quart.,"  XXII,  p.  153  (1901). 


SPECIAL  METHODS   OF  ASSAY  377 

scorified  with  30  to  40  grams  of  lead.  This  gives  lower  gold 
results  but  more  silver  than  the  following: 

No.  4.     W.  Magenau's  l  method  for  crucible  fusion: 

Zinc  precipitate   ^ff  assay  ton 

Dry  soda  carbonate 5  grams 

Borax  glass 2       " 

Silica    5      " 

Litharge 70      " 

Flour   1       " 

Salt  cover. 

Carbonaceous  Residues  (left  in  retorts  after  distillation  of  Zinc). — 
K.  Sander 2  gives  a  method  for  assaying  the  residue  remaining 
\n  the  muffles  after  zinc  distillation.  This  residue  contains  lead 
and  a  large  amount  of  carbon,  and  offers  difficulties  in  the  ordi- 
nary scorification  and  crucible  assays.  He  gives  a  preliminary 
oxidation  as  follows:  The  mixture 

Powdered  residue 20  grams 

Potassium  nitrate    40      " 

Sodium  peroxide    10      " 

is  mixed  with  an  iron  spatula  and  gradually  introduced  into  a 
red-hot  iron  crucible.  After  the  violent  action  has  ceased,  the 
following  flux  is  added: 

Soda 14  parts 

Calcined  borax     8      " 

Litharge 10      " 

Argol   2      " 

Pour  when  tranquil.  The  results  quoted,  however,  are  in  general 
lower  than  those  obtained  by  scorification. 

i"Min.  and  Sci.  Press,"  LXXX,  p.  464  (1900). 
a"  Zeit.  fur  Angew.  Chem.,"  XV,  p.  32  (1902). 


SECTION  IV 
ASSAY   OF   GOLD   AND   SILVER   BULLION 

(A)  FIRE  ASSAY  METHOD 

Sampling:  Dip-samples.  —  The  generally  accepted  opinion  is 
that  the  most  accurate  method  of  sampling  bullion  is  by  means 
of  what  is  known  as  a  "dip-sample."  This  is  taken  from  the 
crucible  or  smelting-furnace  while  the  metal  is  in  a  molten  con- 
dition, immediately  before  pouring.  The  bath  of  metal  is  first 
well  stirred  with  an  iron  bar  (rabbling-iron)  somewhat  flattened 
at  the  end,  and  a  small  portion  of  the  metal  is  taken  out  by  means 
of  a  plumbago  spoon,  held  by  a  pair  of  tongs.  The  dipper  used 
is  often  a  section  cut  from  an  old  graphite  crucible.  When  the 
dip-sample  is  poured  there  should  be  a  thin  layer  of  slag  over  the 
molten  metal  to  prevent  oxidation.  The  dip-sample  may  be 
either  poured  into  a  small  mold  and  subsequently  flattened  and 
cut  into  pieces,  or  it  may  be  granulated  by  pouring  into  water. 

Drill-Samples.  —  Samples  are  also  very  frequently  taken  by 
drilling  one  or  more  holes  in  the  bars  after  casting.  These  "  drill- 
samples  "  are  usually  taken  by  means  of  a  small  vertical  machine 
drill,  which  is  caused  to  revolve  with  considerable  speed,  cutting 
out  fine  turnings  of  the  metal.  A  common  plan  is  to  take  one 
drilling  near  a  corner  of  the  bar  and  the  other  at  the  middle  of 
the  opposite  side,  each  hole  passing  half-way  through  the  bar. 
In  bars  containing  much  base  metal,  there  is  often  a  marked 
difference  in  the  composition  of  the  central  and  superficial  por- 
tions, owing  to  the  phenomenon  of  liquation  which  occurs  during 
the  cooling  of  the  metal. 

Cut-Samples.  —  Samples  are  also  sometimes  taken  by  chipping 
fragments  from  the  corners  or  edges  of  bars,  but  this  procedure 
can  only  give  correct  results  when  no  liquation  has  occurred. 
In  general  it  is  not  to  be  recommended.  The  results  obtained  by 
Stockhausen1  showed  that  drill-samples  gave  a  higher,  and  cut- 

i  "  Proc.  Chem.,  Met.  and  Min.  Soc.  of  South  Africa,"  II,  pp.  46-48. 

378 


ASSAY  OF   GOLD  AND  SILVER  BULLION  379 

samples  from  the  edges  and  corners  a  lower,  result  than  dip- 
samples  from  the  same  bars,  and  also  that  the  cut-samples  ex- 
hibit much  greater  fluctuations  than  either. 

Preparation  of  Samples.  —  The  samples  must  be  carefully 
examined  before  weighing,  and  any  particles  of  slag  or  other 
extraneous  matter  which  may  have  been  accidentally  mixed  with 
them  are  removed.  Occasionally  it  may  be  necessary  to  cut  them 
up  finer;  this  may  be  done  by  hammering  the  fragments  and 
cutting  with  a  clean  pair  of  scissors;  when  the  material  is  brittle, 
as  with  some  qualities  of  cyanide  bullion,  it  may  be  further 
reduced  by  grinding  in  an  agate  mortar. 

Weighing-in.  —  The  sample  is  next  spread  out  on  a  clean  sheet 
of  paper  and  the  charge  weighed.  This  charge  is  usually  500  mg., 
and  the  bullion  taken  may  be  either  adjusted  to  this  exact  amount, 
by  clipping  or  filing  the  fragments,  or  an  approximate  amount  may 
be  taken  and  its  exact  weight  determined  and  recorded.  With  a 
good  assay  balance  the  correct  weight  may  be  determined  within 
0.01  mg.,  but  this  degree  of  accuracy  is  commonly  not  required; 
for  ordinary  purposes  it  is  sufficient  to  weigh  to  0.05  mg. 

Addition  of  Lead.  —  When  the  portion  of  bullion  for  assay  has 
been  weighed  it  is  at  once  transferred  by  means  of  a  fine  brush 
to  a  small  capsule  of  lead-foil.  The  weight  of  lead  to  be  used 
depends  largely  on  the  nature  of  the  impurities  contained  in  the 
bullion,  as  does  also  the  question  whether  scorification  should 
be  employed  or  not.  In  an  ordinary  case  about  four  times  the 
weight  of  the  bullion  taken  (i.e.,  about  2  grams  of  lead-foil)  will 
suffice.  With  certain  kinds  of  base  bullion,  particularly  such  as 
contain  arsenic,  antimony,  selenium  or  tellurium,  a  much  larger 
amount  may  be  necessary,  say  15  grams. 

Additions  of  Copper  and  Silver.  —  When  the  bullion  contains 
no  copper,  it  is  advisable  to  add  a  small  amount,  say  about  20  to 
30  mg.  in  each  assay,  which  prevents  "  spitting  "  after  the  cupella- 
tion.  When  the  amount  of  silver  is  insufficient  for  parting  the 
gold  (i.e.,  less  than  about  two  and  a  quarter  times  the  weight  of 
gold  present),  it  is  necessary  to  add  a  sufficient  quantity  of  silver 
to  the  assay  to  make  up  this  difference.  When  the  bullion  is  to  be 
assayed  for  both  silver  and  gold,  the  most  satisfactory  method  is 
to  make  these  determinations  on  separate  portions.  In  many 
cases,  however,  sufficiently  exact  results  are  obtained  by  re- 
cupeling  the  bead  of  mixed  metal,  with  the  addition  of  the  requisite 


380  THE  CYANIDE  HANDBOOK 

amount  of  fine  silver  and  sufficient  lead-foil.  It  is  necessary  to 
ascertain  that  the  lead-foil  used  is  free  from  gold,  and  its  silver 
contents,  if  any,  must  be  determined  and  allowed  for. 

Checks.  —  With  every  batch  of  bullion  assays  one  or  more 
checks  are  added.  These  are  made  by  weighing  out  exact  quanti- 
ties of  pure  gold  and  silver  corresponding  approximately  to  the 
amounts  expected  to  occur  in  the  actual  bullion  assays.  When 
these  are  unknown,  the  approximate  composition  of  the  bullion  is 
determined  by  a  preliminary  trial.  The  gold  is  first  adjusted  by 
cutting  pieces  from  a  thin  sheet  of  proof  gold,  to  within  0.5  mg. 
of  the  theoretical  amount;  the  weight  of  this  quantity  is  then 
determined  as  accurately  as  possible,  say  to  0.01  mg.  It  is  then 
transferred  to  a  small  lead  capsule  (a  sheet  of  lead-foil  coiled  into 
a  small  conical  pocket  answers  the  purpose).  The  amount  of 
silver  judged  to  be  present  in  500  mg.  of  the  bullion  is  then  weighed 
out,  together  with  an  additional  quantity  to  allow  for  volatiliza- 
tion and  absorption  in  the  muffle;  this  extra  amount  depends  upon 
the  position  the  assays  are  to  occupy  in  cupellation  and  the  tem- 
perature at  which  this  operation  is  to  be  carried  out.  The  silver 
is  adjusted  to  within  2  mg.  of  the  amount  theoretically  required, 
the  exact  weight  being  then  determined  to  within  0.02  mg.  It  is 
then  added  to  the  capsule  containing  the  gold.  It  is  usual  to 
add  also  a  small  quantity  of  copper,  and  it  is  desirable,  at  least 
occasionally,  to  ascertain  the  effect  of  adding  other  ingredients 
corresponding  to  the  amounts  present  in  the  bars  to  be  assayed. 
In  an  ordinary  case  15  to  20  mg.  of  copper  may  be  added. 

Losses  of  Silver  in  Cupellation.  —  A  series  of  tests  were  made 
by  the  writer  on  known  weights  of  gold  and  silver,  approximately 
400  rng.  Ag  to  60  mg.  Au,  with  about  15  grams  lead-foil  in  each 
case,  cupeling  in  an  ordinary  fire-clay  muffle,  size  "  J,"  with  char- 
coal as  fuel,  and  using  4  cross-rows  of  3  cupels  each.  The  extra 
silver  required  was  shown  by  these  tests  to  be  approximately  as 
follows : 


Cupels  used 
Size 

Morganite.    No.  5 
Loss  of  Silver 
Mg. 

Bone-ash.    No.  5 
Loss  of  Silver 
Mg. 

First  row  (at  back)  

6-8 

11-14 

Second  row 

5-7 

Q   10 

Third  row 

4-6 

7  10 

Fourth  row  (in  front)  

3-5 

5-S 

ASSAY  OF  GOLD  AND  SILVER   BULLION  381 

(See  remarks  on  this  subject  in  Section  II,  a.) 
Position  of  Checks.  —  The  lead  packets  containing  the  weighed 
bullion  or  check  pieces  are  rolled  up  and  placed  in  their  proper 
positions  in  a  suitable  tray.  Generally,  two  checks  with  each 
muffle  charge  will  be  sufficient,  but  where,  as  in  the  experiment 
quoted  above,  the  differences  of  temperature  in  different  parts 
of  the  muffle  are  considerable,  it  is  as  well  to  use  a  check  with 
each  row,  the  two  remaining  places  in  the  row  being  occupied 
by  duplicates  of  the  same  assay  sample.  In  order  to  equalize 
the  effects  of  any  possible  differences  of  temperature  in  various 
parts  of  the  muffle,  the  position  of  the  checks  may  be  altered  with 
each  batch  of  assays,  as  shown  in  the  following  arrangements, 
where  the  numbers  1,  2,  etc.,  represent  the  bar  assays,  and  the 
letters  a,  b,  c,  d  the  checks: 

No.  1  No.  2  No.  3  No.  4 

all  lal  lla  lal 

262  622  262  226 

33c  3   c   3  c33  3c3 

4   d   4  4   4   d  4   d   4  d   4   4 

In  an  ordinary  muffle-furnace  it  will  be  found  that  the  tem- 
perature is  lower  and  the  losses  of  silver  therefore  less  in  the  cen- 
tral line  of  the  muffle  than  at  the  sides,  and  the  back  rows  are  also 
considerably  hotter  than  the  front. 

Cupellation.  —  The  cupels  are  heated  for  some  time  in  the 
muffle  before  introducing  the  assay  pieces.  Claudet 1  recommends 
baking  in  the  furnace  for  about  an  hour,  but  in  most  cases  a 
shorter  time  would  seem  to  be  sufficient.  The  safest  plan  is  to 
introduce  a  small  piece  of  pure  lead  into  each,  when  the  cupels 
appear  to  be  hot  enough.  When  this  has  melted  and  begins  to 
cupel  freely  the  assay  pieces  and  checks  may  be  transferred  by 
means  of  cupel-tongs  from  the  tray  to  the  corresponding  cupels  in 
the  muffle,  each  packet  being  dropped  carefully  into  its  proper 
cupel,  where  it  is  at  once  absorbed  in  the  bath  of  molten  lead. 
The  furnace,  where  coke  or  charcoal  is  used,  should  be  well  filled 
up  with  fuel,  and  a  moderate  red  heat  maintained  throughout 
the  operation.  Towards  the  end  the  door  should  be  closed  as  a 
somewhat  higher  temperature  is  required.  To  secure  greater 
uniformity  of  temperature,  a  block  of  red-hot  coke  or  charcoal 

i  Inst.  Min.  and  Met.  Bull  No.  27,  p.  16  (Dec.  13,  1906). 


382  THE  CYANIDE  HANDBOOK 

is  sometimes  placed  at  the  mouth  of  the  muffle.  Another  plan  is 
to  surround  the  assay  pieces  by  rows  of  empty  cupels,  so  that  the 
actual  cupellation  is  carried  on  only  in  the  central  part  of  the 
muffle.  The  time  occupied  in  cupellation  will  vary  from  ten 
minutes  to  half  an  hour  or  more,  according  to  the  weight  of  lead 
and  the  temperature  at  which  the  operation  is  conducted.  When 
approaching  the  finish,  a  play  of  iridescent  colors  is  noticed  on 
the  surface  of  the  beads;  these  are  interference  colors  produced  by 
the  very  thin  transparent  film  of  litharge  surrounding  the  beads. 
The  cupels  are  then  withdrawn  in  their  proper  order  and  placed 
for  a  few  minutes  at  the  mouth  of  the  muffle  until  the  beads  have 
solidified.  This  is  accompanied  by  a  sudden  flash  of  light. 

If  the  cooling  has  been  too  sudden,  this  process  may  be  accom- 
panied by  violent  projection  of  particles  of  silver,  by  " sprouting" 
or  "vegetating"  (i.e.,  the  formation  of  irregular  processes  pro- 
jecting from  the  surface  of  the  bead).  These  effects  are  generally 
ascribed  to  the  sudden  ejection  of  occluded  oxygen  absorbed  by 
the  molten  silver  during  the  cupellation.  When  the  proper  con- 
ditions are  carefully  attended  to,  this  will  not  occur,  and  the  beads 
when  withdrawn  from  the  muffle  will  show  a  perfectly  smooth, 
bright  surface. 

The  sizes  of  cupels  from  No.  3  to  No.  5  are  most  commonly 
used  for  bullion  work.  Various  materials  are  used,  several  sub- 
stitutes for  bone-ash  having  been  extensively  adopted  of  late 
years. 

Scarification.  —  Where  the  bullion  is  very  base,  and  especially 
when  it  contains  ingredients  which  would  be  liable  to  crack  or 
corrode  the  cupels,  a  preliminary  operation  is  resorted  to.  In- 
stead of  transferring  the  lead  packets  direct  to  the  cupels,  they 
are  placed  in  small  previously  heated  scorifiers  (l\  in.  to  1J  in. 
diameter),  with  the  addition  of  a  very  small  quantity  (say  0.1 
gram)  of  borax.  Oxidation  of  the  base  metals  then  takes  place, 
and  the  molten  oxides  form  fusible  silicates  with  the  material  of 
the  scorifier  itself,  producing  a  slag  which  floats  on  the  surface 
of  the  molten  lead.  The  details  of  the  process  have  been  already 
described  in  Section  III  (a).  When  the  operation  is  complete, 
the  scorifiers  are  taken  out  and  their  contents  poured  into  small 
molds  previously  warmed.  The  clean  lead  button  is  detached 
when  sufficiently  cool,  and  cupeled  in  the  ordinary  way.  The 
slag  should  be  uniform;  when  chiefly  consisting  of  lead  silicate,  it 


ASSAY  OF  GOLD  AND  SILVER  BULLION  383 

has  a  yellowish-brown  color,  but  may  be  stained  dark  brown  by 
iron,  or  green  by  copper,  manganese,  etc. 

Cleaning  and  Flattening  the  Beads.  —  The  beads  are  detached 
from  the  cupels  by  means  of  pliers  and  squeezed  with  some  force 
to  loosen  any  adhering  matter.  A  convenient  method  of  clean- 
ing the  bead  is  to  hold  it  edgewise  with  a  small  pair  of  steel  forceps, 
striking  it  once  or  twice  on  the  edge  with  a  smooth-faced  hammer 
on  a  smooth,  clean  anvil.  The  rough  under  surface,  where  the 
bead  was  in  contact  with  the  cupel,  may  then  be  easily  cleaned 
todth  a  wire  scratch-brush.  The  bead  is  then  flattened  by  one  or 
two  blows  of  the  hammer.  Small  beads  containing  much  silver 
may  quite  well  be  hammered  out  to  about  1  c.m.  diameter.  The 
hammer  and  anvil  for  this  purpose  should  be  kept  perfectly  clean 
and  polished,  and  used  exclusively  for  hammering  assay  beads. 

Weighing  Fine  Metal.  — •  The  beads  are  now  weighed,  this 
weight  being  recorded  as  "fine  metal";  if  the  operation  has  been 
properly  conducted,  this  is  the  sum  of  the  gold  and  silver,  less 
whatever  losses  have  taken  place  by  volatilization  and  absorption 
in  the  cupels  during  cupellation.  It  is  generally  sufficient  to 
weigh  to  0.02  mg.  The  variation  in  the  adjustment  of  the  balance 
may  be  corrected  as  described  in  Section  II  (6),  or  the  method  of 
"  substitution  "  may  be  used  (in  which  the  bead  is  first  placed  in 
the  right-hand  pan  of  the  balance,  and  then  counterpoised  by 
pieces  of  metal  or  rough  weights  in  the  left-hand  pan) .  The  bullion 
bead  is  then  removed  and  accurate  weights  added  on  the  right 
until  equilibrium' is  obtained,  the  final  adjustment,  of  course, 
being  made  with  the  rider. 

Annealing  and  Rolling.  —  The  beads  are  generally  annealed 
by  heating  to  dull  redness  on  fire-clay  tiles,  or  in  a  small  spirit 
or  gas  flame,  and  rolled  into  strips  about  3  in.  in  length  (fillets) 
by  passing  between  smooth  steel  rolls.  The  most  convenient 
form  of  rolls  have  a  single  adjusting  screw,  working  in  such  a 
way  that  the  rolls  always  remain  exactly  parallel;  when  there  are 
two  screws,  this  is  difficult  to  secure.  The  rolls  are  first  loosened 
so  as  to  allow  the  metal  to  pass  through  without  much  force; 
then  they  are  gradually  tightened,  so  that  the  strip  becomes  some- 
what longer  and  thinner  each  time  it  is  passed  through.  The 
edges  should  be  smooth  and  show  no  signs  of  frilling  or  cracks. 
After  rolling,  the  fillets  are  again  annealed  and  loosely  coiled, 
taking  care  to  leave  the  rougher  side,  corresponding  to  the  bottom 


384  THE  CYANIDE  HANDBOOK 

of  the  bead  on  the  cupel,  on  the  outer  side  of  the  roll,  so  as  to  be 
more  easily  attacked  by  the  acid.  Beads  containing  a  large  per- 
centage of  silver  (say  5  to  7  times  the  weight  of  the  gold)  may 
quite  well  be  parted  without  rolling  out,  provided  they  are  well 
flattened  by  hammering  to  at  least  1  cm.  diameter. 

Parting.  — •  This  operation  is  usually  carried  out  in  special 
glass  vessels  (parting-flasks)  having  a  somewhat  lengthened  bulb 
and  a  long  narrow  neck.  The  method  of  using  these  is  described 
in  Section  II  (6).  Equally  good  results  may,  with  care,  be  ob- 
tained by  using  porcelain  crucibles  of  somewhat  large  size  (say 
4J  cm.  diameter  by  3  cm.  deep).  Where  large  numbers  of  bullion 
assays  are  made  at  a  time,  as  in  mints,  etc.,  it  is  customary  to  use 
a  platinum  parting  apparatus,  consisting  of  a  tray  with  a  number 
of  perforated  recesses  ("thimbles"),  in  which  the  rolled  assay 
beads  ("  cornets ")  are  placed.  The  whole  tray  is  immersed  in 
a  platinum  vessel  containing  nitric  acid,  so  that  all  the  cornets 
receive  uniform  treatment. 

Arthur  C.  Claudet  l  gives  the  following  description  of  parting 
with  the  platinum  apparatus: 

"  The  cornets  are  placed  in  a  platinum  tray,  capable  of  holding 
sixty  comets,  in  their  respective  thimbles.  Twenty-five  ounces  of 
nitric  acid,  sp.  gr.  1 160°,  are  put  into  No.  1  platinum  boiler,  and  the 
tray  of  cornets  immersed  in  it.  The  boiling  is  continued  till  no 
more  nitrous  fumes  are  observed.  The  tray  is  then  taken  out  and 
drained  from  the  acid  liquor,  then  washed  in  distilled  water  and 
immersed  in  No.  2  boiler,  containing  25  oz.  nitric  acid,  sp.  gr. 
1250°;  boiling  is  continued  for  20  minutes;  the  tray  is  then  re- 
moved from  the  boiler  and  the  acid  liquor  drained  off;  the  tray  is 
immersed,  without  washing,  in  No.  3  boiler,  containing  25  oz. 
nitric  acid,  sp.  gr.  1250,  and  boiling  continued  for  20  minutes. 
The  tray  is  then  removed,  drained,  washed  twice  with  distilled 
water,  drained  again,  and  dried  quietly  over  a  gas-burner  covered 
with  wire  gauze.  The  tray  is  placed  in  the  muffle-furnace  on  a 
suitable  revolving  platform  to  anneal,  and  when  the  cornets  are 
thoroughly  red-hot,  is  withdrawn.  The  cornets  are  then  of  a 
bright  gold  color." 

In  the  office  of  a  mine  or  cyanide  plant,  where  such  expensive 
apparatus  is  commonly  not  available,  the  following  method  will 
generally  be  found  to  work  satisfactorily.  The  flattened  beads  or 

>I.  M.  M.,  Bull  No.  27,  Dec.  13,  1906,  p.  17. 


ASSAY  OF   GOLD   AND  SILVER  BULLION  385 

cornets  are  placed  in  porcelain  crucibles  of  convenient  size,  sup- 
ported on  a  perforated  metal  plate  over  a  uniform  source  of  heat, 
such  as  a  large  oil-stove,  and  15  c.c.  of  "weak  acid"  poured  over 
each.  The  weak  acid  is  prepared  by  diluting  1  part  of  pure  nitric 
acid  (sp.  gr.  1.42)  with  7  parts  of  water  (i.e.,  12.5  per  cent,  by 
volume  of  concentrated  acid).  After  the  cornets  have  been  well 
boiled,  the  lamp  is  turned  down,  the  acid  being  kept  hot,  but  not 
actually  boiling,  for  say  15  minutes,  after  which  the  liquid  is  again 
boiled  till  quite  colorless,  and  until  the  bubbles  given  off  no  longer 
show  the  slightest  appearance  of  brown  fumes.  If  on  cooling  for 
a  moment  a  rapid  evolution  of  small  bubbles  still  takes  place,  the 
boiling  is  further  continued,  but  usually  about  20  minutes'  treat- 
ment in  the  weak  acid  is  sufficient.  This  acid  is  then  drained  off 
and  poured  away  into  the  silver  residue  bottle.  The  cornets  are 
washed  once  with  distilled  water,  and  15  c.c.  of  " strong"  acid 
poured  on.  The  strong  acid  is  prepared  by  mixing  3  volumes  of 
pure  nitric  acid  (sp.  gr.  1.42)  with  1  volume  of  water,  and  thus 
contains  75  per  cent,  by  volume  of  concentrated  acid.  The  liquid 
is  raised  cautiously  to  the  boiling-point;  the  lamp  is  then  turned 
down  for  say  25  minutes,  thus  keeping  the  crucibles  hot  but  not 
actually  boiling,  and  adding  fresh  acid  if  necessary.  At  the  finish 
the  temperature  is  again  raised  to  the  boiling-point.  The  time 
allowed  for  strong  acid  treatment  is  usually  about  30  minutes. 
For  good  results  it  is  necessary  to  boil  thoroughly  in  both  acids. 

Precautions.  —  Evaporation  to  dryness  must  be  carefully 
avoided,  especially  during  the  weak-acid  treatment,  for  if  the 
cornets  are  heated  sufficiently  at  that  stage  to  cause  them  to 
acquire  a  natural  gold  color,  it  is  afterwards  impossible  to  extract 
the  residual  silver  by  the  strong-acid  treatment,  and  the  result 
will  be  too  high. 

By  the  treatment  above  described,  beads  containing  originally 
60  to  80  mg.  of  gold  and  350  to  420  mg.  of  silver  usually  remain 
unbroken.  When  the  proportion  of  silver  is  much  larger  they 
break  to  pieces  and  some  care  is  necessary  to  avoid  loss.  Too 
violent  boiling  must  also  be  carefully  guarded  against,  as  this  is 
liable  to  cause  spurting,  especially  during  the  strong  acid  treat- 
ment, and  may  result  in  the  cornet  suddenly  breaking  in  pieces, 
in  which  case  fragments  are  likely  to  be  projected  out  of  the 
crucible. 

Solvent  Action  of  Nitric  Acid  on  Gold.  —  Contradictory  opinions 


386  THE  CYANIDE  HANDBOOK 

are  expressed  by  different  writers  on  this  subject.  (See  Section 
II,  b.)  Some  maintain  that  neither  nitric  nor  nitrous  acids  by 
themselves  are  capable  of  dissolving  gold.  It  has  been  observed, 
in  parting  cornets  containing  a  rather  high  percentage  of  silver, 
with  nitric  acid  perfectly  free_from  chlorides,  that  on  diluting  the 
clear  liquid  containing  the  dissolved  silver,  either  with  cold  acid 
or  water,  a  dark  purplish  turbidity  was  formed.  On  boiling,  the 
liquid  became  clear  again,  but  a  blackish  scum  was  formed  which 
seems  to  consist,  at  least  partially,  of  finely  divided  gold. 

Igniting  the  Cornets.  —  After  pouring  off  the  strong  acid,  the 
cornets  are  washed  and  the  inside  surface  of  the  crucible  carefully 
rinsed  out  with  distilled  water.  This  operation  is  repeated  at 
least  twice.  The  crucibles  are  then  replaced  on  the  perforated 
frame  over  the  lamp  and  allowed  to  dry  for  a  few  minutes  at  a 
moderate  heat.  They  are  then  ignited  by  being  placed  for  a 
minute  or  so  in  a  muffle  at  a  dull  red  heat,  or  by  holding  the  cru- 
cibles in  the  flame  of  a  blast  lamp  until  they  acquire  a  bright 
golden  color.  Care  must  be  taken  not  to  heat  so  intensely  as  to 
fuse  the  gold. 

Weighing  Gold  Cornets.  —  When  cool,  the  gold  cornets  are 
weighed  on  the  fine  assay  balance,  recording  the  correct  weight 
to  0.01  mg.  A  good  assay  balance  will  weigh  to  0.005  mg.,  but 
this  degree  of  accuracy  is  not  usually  necessary.  The  cornets 
must  be  a  good  color;  if  pale,  it  is  a  sign  that  they  contain  undis- 
solved  silver.  The  adjustment  of  the  balance  must  be  carefully 
attended  to,  and  corrected,  if  necessary,  as  described  under  ore 
assaying.  It  is  advisable  to  verify  the  correctness  of  the  adjust- 
ment after  every  two  or  three  weighings  by  allowing  the  balance 
to  swing  with  the  pans  empty,  a  special  rider  on  the  left  arm  of 
the  beam  being  used  to  correct  any  inequality  in  the  swings. 
Errors  from  this  source  may  also  be  corrected  by  the  method  of 
substitution  above  noted. 

Accuracy  of  Assay  Weights.  —  It  is  necessary  to  carefully 
examine  the  weights  used,  and  to  determine  their  true  relative 
value  with  reference  to  the  500  mg.  weight  used  for  weighing  the 
bullion-charges,  as  the  sets  supplied,  even  by  firms  of  high  stand- 
ing, are  by  no  means  absolutely  correct. 

Milliemes.  —  Some  assayers  use  the  "  millieme "  system,  in 
which  the  500  mg.  weight  is  marked  1000,  and  its  subdivisions 
numbered  in  milliemes,  or  half-milligrams.  This  has  the  advan- 


ASSAY  OF  GOLD   AND  SILVER   BULLION  387 

tage  of  giving  the  "fineness"  on  a  charge  of  0.5  gram  of  bullion 
directly,  without  calculation,  but  is  very  confusing  if  the  weights 
are  used  for  other  purposes,  as  the  numbers  are  apt  to  be  mis- 
taken for  milligrams. 

The  fineness  of  the  bullion  is  generally  reported  in  parts  per 
1000.  As  500  mg.  are  taken  for  each  assay,  it  is  merely  necessary 
to  multiply  the  result  by  two  to  obtain  the  fineness. 

Correction  of  Results  by  Checks.  —  A  correction  is  required  to 
be  made  for  losses  of  gold  and  silver  in  cupellation,  and  for  silver 
retained  in  the  cornets  after  parting.  In  the  gold  assay,  the 
weight  actually  obtained  is  the  net  result  of  the  losses  in  the  first 
operation  and  the  gains  in  the  second.  It  is  assumed  that  the 
fine  gold  used  in  the  check  has  undergone  the  same  losses  and 
gains  as  that  from  the  bar.  This  is  only  strictly  true  when  the 
check  is  very  closely  of  the  same  composition  as  the  bullion  to  be 
assayed,  and  has  been  subjected  to  .precisely  similar  treatment. 
If  the  check,  as  is  usually  the  case,  shows  an  increase  of  weight, 
the  amount  of  this  increase  is  deducted  from  the  weight  of  gold 
obtained  from  the  bars  adjoining  that  particular  check  in  the 
muffle;  if  the  check  has  diminished,  the  amount  of  such  decrease 
is  added  to  the  weight  of  gold  from  each  bar  assay. 

Amount  of  Surcharge.  —  According  to  A.  C.  Claudet1  the 
amount  of  surcharge  in  gold  bullion  assays  may  vary  from  0.7  to 
1.0  per  millieme  (i.e.,  0.35  to  0.5  mg.  on  an  assay  of  500  mg.)  and  is 
always  an  increase  on  the  amount  taken  for  the  check;  this  amount 
must  therefore  be  deducted  from  the  weight  of  the  cornet  in  each 
bar  assay.  Professor  W.  Gowland2  stated,  in  the  discussion  on 
Claudet's  paper,  that  the  surcharge  at  the  Mint  of  Japan  varied 
during  6  months  from  0.5  to  0.7,  averaging  0.55.  He  also  remarks 
that  a  small  surcharge  indicates  that  the  cupellation  has  been 
carried  out  at  too  high  a  temperature,  and  that  in  such  a  case  the 
assay  should  be  repeated,  still  more  so  if  there  should  be  no  sur- 
charge or  a  loss  on  the  checks.  These  figures,  however,  all  prob- 
ably refer  to  bullion  consisting  chiefly  of  gold.  According  to  T.  W. 
Wood,3  the  surcharge  varies  according  to  the  relative  proportion 
of  gold  and  silver,  and  with  bullion  consisting  chiefly  of  silver  the 
gold  checks  usually  show  a  loss.  The  present  writer's  experience 

il.  M.  M.,  Bull.  No.  27,  p.  17. 

2  Ibid.,  Bull.  No.  28,  p.  29. 

3"  Proc.  Chem.,-Met.  and  Min.  Soc.  of  South  Africa,"  II,  p.  3. 


388  THE  CYANIDE  HANDBOOK 

with  bullion  averaging  about  800  in  silver  and  60  to  70  in  gold 
was  that  the  surcharge  rarely  exceeded  ±0.4  per  1000  (i.e.,  0.2 
mg.  on  500  mg.). 

Under  normal  conditions  the  silver  always  shows  a  loss,  so 
that  the  correction  indicated  by  the  check  has  to  be  added  to  the 
silver  found.  It  occasionally  happens  that  the  front  row  in  the 
muffle  shows  an  apparent  increase  in  silver.  This  is  due  to  reten- 
tion of  lead ;  in  such  cases  the  correction  cannot  be  safely  applied 
and  the  assays  must  always  be  repeated,  using  a  somewhat 
higher  temperature. 

Examples  of  Corrections  for  Bullion  Assays.  —  (a)  Gold  Bullion 
(e.g.,  battery  gold);  500  mg.  taken  for  assay,  in  duplicate. 

Gold:  Silver: 

mg.  mg. 

Taken  for  check 284.52         207.85 

Found..  284.86         206.42 


Correction —.34  + 1.43 

Gold: 

Bar  assay:                                              Found  Corrected 

284.93  284.59 

284.79  284.45 


Silver: 

Bar  assay:  Found  Corrected 

206.37  207.80 

206.25  207.68 

Gold  Silver 

Mean  Fineness 569.04  415.48 

(b)  Silver  Bullion  (Cyanide) .  — 

Gold:  Silver: 

mg.  mg. 

Taken  for  check 76.79  397.59 

Found 76.88  391.97 

Correction -.09  +5.62 

Gold: 

Bar  assay:  Found  Corrected 

76.70          76.61 
76.68          76.59 


ASSAY  OF   GOLD   AND   SILVER  BULLION 

Silver: 
Found  Corrected 

391.80    397.42 
392.76    398.38 

Gold  Silver 

Mean  fineness 153.2          795.8 

(B)  VOLUMETRIC  METHODS 

There  are  two  methods  in  general  use  for  determining  the 
silver  in  bullion;  several  others  have  been  proposed,  but  these  two 
only  need  be  considered  here.  They  are:  (1)  Gay-Lussac's 
method;  (2)  Volhard's  method. 

(1)  Gay-Lussac's  Method.  —  This  method  depends  on  the  fact 
that  silver  is  precipitated  by  solutions  of  sodium  chloride  as  a 
white  chloride,  insoluble  in  dilute  acid  solutions;  the  only  other 
metals  precipitated  under  the  same  conditions  being  lead  and 
mercury.  Since  the  chloride  coagulates  and  settles  rapidly  on 
agitating  the  solution,  the  finishing  point  of  the  reaction  may  be 
found  by  noting  the  point  when  fresh  additions  of  salt  solution 
fail  to  produce  any  further  precipitate.  It  has  been  found, 
however,  that  silver  chloride  is  slightly  soluble  in  the  sodium 
nitrate  produced  in  the  reaction: 

NaCl  +  AgNO3  =  NaNO3  +  AgCl. 

Hence  the  true  finishing  point  occurs  slightly  before  the  point  at 
which  fresh  NaCl  ceases  to  give  a  precipitate.  In  fact,  at  or  near 
the  point  of  exact  correspondence  the  solution  will  give  a  pre- 
cipitate of  AgCl  if  either  salt  or  silver  solution  be  added;  the  true 
end-point  may  be  found  by  determining  (1)  the  point  at  which 
NaCl  ceases  to  give  a  precipitate,  (2)  the  point  at  which,  after  a 
slight  excess  of  NaCl  has  been  added,  a  corresponding  solution 
of  AgNO3  ceases  to  give  a  precipitate,  and  taking  the  mean  of 
the  two  results.  The  amount  of  AgCl  dissolved  in  this  way  de- 
pends on  the  temperature  and  degree  of  dilution  of  the  solutions. 
A  simpler  method  is  to  determine  the  finishing  point,  by  means 
of  an  accurately  prepared  salt  solution,  for  different  measured 
quantities  of  a  silver  solution  of  known  strength;  after  a  number 
of  such  observations  have  been  made,  a  factor  can  be  deduced 
which  will  give  the  proper  correction  for  any  reading.  The  solu- 
tions commonly  used  for  assays  by  this  method  are: 


390  THE  CYANIDE  HANDBOOK 

1.  A   "standard"   salt  solution,   made  by  dissolving  5.4202 
grams  of  the  purest  obtainable  dry  sodium  chloride  in  distilled 
water,  and  making  up  to  a  liter;  1  cc.  of  this  solution  =  .01  gram 
Ag.     The  pure  salt  is  best  prepared  by  neutralizing  pure  sodium 
carbonate  or  bicarbonate  with  hydrochloric  acid,  evaporating  to 
dryness,  and  igniting. 

2.  A  salt  solution,  prepared  from  the  above  of  exactly  one- 
tenth  the  strength,  known  as  the  "decimal"  salt  solution;  1  cc. 
of  this  solution  =  .001  gram  Ag. 

3.  A  solution  of  silver  nitrate  corresponding  exactly  to  the  deci- 
mal salt  solution,  that  is,  containing  1  gram  of  Ag  dissolved  in  pure 
nitric  acid,  heated  to  expel  nitrous  fumes  and  diluted  to  a  liter. 

In  making  a  test,  the  quantity  of  bullion  taken  must  be  such 
that  it  contains  very  slightly  more  than  1  gram  of  silver,  this 
being  ascertained  by  a  previous  approximate  assay.  This  is 
introduced  into  a  stoppered  bottle  and  dissolved  in  nitric  acid, 
heating  on  the  water-bath  till  completely  dissolved,  after  which 
the  stopper  is  removed  and  the  nitrous  fumes  dispelled  by  blowing 
through  a  bent  tube.  Then  100  cc.  of  the  standard  salt  solution 
are  added  by  means  of  an  accurately  graduated  pipette,  so  that 
exactly  1  gram  of  silver  is  precipitated.  The  stopper  is  replaced 
and  the  bottle  shaken,  being  kept  in  the  dark  as  much  as  possible, 
until  the  silver  chloride  settles  clear.  The  decimal  salt  solution  is 
then  added,  a  little  at  a  time,  as  long  as  a  further  drop,  after  agi- 
tation and  settling,  continues  to  produce  a  precipitate.  A  me- 
chanical device  is  often  used  for  the  agitation  of  the  bottles,  so 
arranged  that  they  are  kept  dark,  since  silver  chloride  is  rapidly 
acted  upon  and  decomposed  by  exposure  to  light. 

With  care,  this  method  yields  very  accurate  results,  but  the 
necessity  of  waiting  after  each  addition  of  the  test  solution  for  the 
settlement  of  the  precipitate  renders  it  very  tedious. 

(2)  Volhard's  Method.  —  This  depends  on  the  fact  that  silver 
in  nitric  acid  solution  is  precipitated  by  solutions  of  a  soluble 
thiocyanate  (sulphocyanide),  and  that  if  a  ferric  salt  be  present 
the  red  ferric  thiocyanate  is  decomposed  and  the  color  destroyed 
as  long  as  silver  is  in  excess.  The  reactions  are: 

KCNS  +  AgNO3  =  KNO3  +  AgCNS. 
3KCNS  +  Fe(NO3)3  =  3KNO3  +  Fe(CNS)3. 

As  soon  as  all  the  silver  is  precipitated,  the  red  color  remains 
permanent. 


ASSAY  OF   GOLD   AND  SILVER   BULLION  391 

Standard  and  decimal  solutions  of  potassium  or  ammonium 
thiocyanate  may  be  prepared,  such  that  1  cc.  =  .01  gram  Ag,  and 
1  cc.  =  .001  gram  Ag,  respectively.1  In  this  case  the  solutions 
cannot  conveniently  be  prepared  by  direct  weighing  of  the  thio- 
cyanate, on  account  of  the  deliquescent  nature  of  the  salt,  but 
may  be  adjusted  by  comparison  with  a  silver  solution  of  exactly 
known  strength. 

With  this  process  also  there  is  a  difficulty  as  to  the  exact  finish- 
ing point,  owing  to  the  fact  that  the  red  ferric  thiocyanate  color 
disappears  very  slowly  and  only  after  continued  agitation  when 
only  a  small  excess  of  silver  is  present.  Various  methods  of 
determining  the  end-point  have  been  suggested,  as  follows : 

1.  A  somewhat  sharper  finish  is  obtained  by  adding  a  slight 
excess  of  thiocyanate,  shaking  thoroughly,  then  cautiously  add- 
ing a  dilute  silver  nitrate  solution  (say  1  cc.  =  .0005  gram  Ag), 
drop  by  drop,  until  the  red  color  just  disappears,  deducting  the 
equivalent  of  AgNO3  used  from  the  thiocyanate  taken. 

2.  Precipitating  the  bulk  of  the  silver  as  chloride  by  means  of 
a  decimal  salt  solution  (as  in  Gay-Lussac's  method),  filtering,  and 
titrating  the  nitrate  only  with  dilute  thiocyanate. 

3.  Adding  a  slight  excess  of  thiocyanate,  estimating  the  amount 
of  this  excess  (or  rather  its  equivalent  in  terms  of  silver)  by 
colorimetric  comparison  with  measured  quantities  of  solution  of 
known  strength  necessary  to  give  a  tint  of  equal  intensity,  and 
deducting  this  from  the  silver  equivalent  of  the  total  thiocyanate 
used.     The  solution  must  be  filtered  before  making  the  compari- 
son.    (See  E.  A.  Smith,  in  I.  M.  M.,  Bull.  No.  28.) 

The  method  may  be  used  in  presence  of  most  of  the  ordinary 
metals,  such  as  lead,  iron,  zinc,  copper,  etc.,  which  may  be  present 
in  considerable  amount  without  affecting  the  result.  The  presence 
of  copper  alters  the  tint  of  the  solution  at  the  finish,  and  hence 
interferes  with  the  colorimetric  method  of  determining  the  end 
point. 

The  writer  finds  it  advisable  to  avoid  filtration.  Where  the 
quantity  of  silver  in  the  solution  is  considerable  (more,  say,  than 
0.1  gram),  it  is  better  to  add  the  thiocyanate  in  slight  excess, 
shake  thoroughly,  allow  to  settle  for  some  time,  decant  the  almost 
clear  liquid  (tinged  red  by  the  ferric  indicator  and  excess  of  thio- 

i  It  is  more  convenient  to  work  with  weaker  solutions,  say  1  cc.  =  .005  gram 
and  1  cc.  -  .0005  gram. 


392  THE  CYANIDE  HANDBOOK 

cyanate)  into  a  separate  vessel,  adding  water,  agitating,  settling 
and  decanting  several  times,  and  titrate  the  whole  liquid  poured 
off  by  means  of  the  dilute  standard  silver  solution  until  the  red 
color  disappears. 


PART  VIII 

ANALYTICAL    OPERATIONS 

IN  this  part  of  the  present  volume,  some  description  will  be 
given  of  the  analytical  methods  required  for  the  examination  of 
such  substances  as  may  occasionally  demand  analysis  in  connec- 
tion with  cyanide  work.  The  subject  is  divided  into  the  follow- 
ing sections: 

I.    Analysis  of  ores  and  similar  siliceous  material,  including 


II.    Analysis  of  bullion  and  other  mainly  metallic  products. 

III.  Analysis  of  cyanide  solutions  after  use  in  ore  treatment. 

IV.  Analysis  of  commercial  cyanide  (solid). 

V.    Analysis  of  sundry  materials  (lime,  coal,  water)  used  in 
the  process. 


SECTION  I 

ANALYSIS  OF  ORES  AND  SIMILAR  SILICEOUS  MATERIAL 

No  attempt  can  be  made  in  a  work  of  this  kind  to  give  minute 
details  of  analytical  methods,  but  a  general  outline  will  be  here 
presented,  with  references  to  standard  works,  where  the  reader 
may  obtain  fuller  information.  In  this  section  the  analysis  will 
be  described  of  such  material  as  might  commonly  be  expected 
to  contain  50  per  cent,  or  more  of  silica.  The  constituents  whose 
determination  is  followed  are  those  which  may  be  of  interest 
and  importance  in  cyanide  work,  and  for  convenience  of  refer- 
ence they  are  arranged  alphabetically,  though  of  course  the 
actual  order  of  analysis  would  be  determined  by  the  nature  of 
the  sample. 

PRELIMINARY  OPERATIONS 

The  operations  of  sampling,  crushing,  and  drying  are  of  at 
least  as  much  importance  in  analysis  as  in  assaying;  in  fact, 
certain  operations  which  are  quite  allowable  in  ordinary  assay 
work  would  not  be  admissible  in  an  analysis. 

Crushing.  —  The  use  of  an  ordinary  iron  pestle  and  mortar 
might  introduce  sufficient  iron,  in  the  form  of  metal  or  oxide,  to 
entirely  vitiate  the  result.  The  metallic  portion  may,  it  is  true, 
be  removed  with  a  magnet,  but  many  minerals  themselves  con- 
tain magnetic  particles,  and  the  magnet  does  not  remove  foreign 
particles  of  oxide  of  iron.  The  crushing  can  only  be  carried  out 
safely  by  means  of  a  well-polished  hard-steel  hammer  and  anvil, 
provided  with  a  guard  to  retain  flying  particles,  followed  by  fine 
grinding  of  a  well-mixed  average  portion  with  an  agate  pestle 
and  mortar. 

Sifting.  —  Metal  sieves  are  liable  to  induce  contamination, 
and  even  sifting  through  cloth  may  give  rise  to  organic  impu- 
rities. In  some  cases,  sifting  is  entirely  unnecessary;  in  others, 
judgment  must  be  used  as  to  whether  the  possible  contamina- 

395 


396  THE  CYANIDE  HANDBOOK 

tion  of  the  sample  is  sufficient  to  necessitate  a  special  determina- 
tion in  an  unsifted  sample  of  the  elements  (iron,  copper,  zinc) 
which  might  arise  from  the  wearing  of  the  screen. 

Drying.  —  The  presence  of  moisture  in  samples  for  analysis 
is  sometimes  overlooked.  Many  siliceous  substances,  when 
finely  divided,  readily  absorb  moisture  from  the  air,  which  adds 
to  their  weight  without  imparting  any  visible  dampness  to  the 
sample.  This  so-called  "hygroscopic  water,"  if  neglected,  will 
cause  unaccountable  variations  in  the  determination  of  the  other 
constituents.  On  this  account  it  is  customary  to  dry  the  por- 
tion of  the  sample  to  be  taken  for  analysis  for  some  hours  at  a 
fixed  temperature  (generally  100°  or  110°  C.),  weighing  at  inter- 
vals in  a  glass-stoppered  bottle,  which  is  of  course  left  open 
during  the  drying,  until  two  consecutive  weighings  agree  within 
sufficiently  narrow  limits.  Another  method  sometimes  employed 
is  to  take  the  crushed  mineral  in  the  undried  condition,  and  weigh 
out,  as  nearly  as  possible  at  the  same  time,  all  the  portions 
required  for  the  different  determinations,  including  one  for  hygro- 
scopic water.  The  percentages  of  the  various  constituents  in 
the  dry  sample  are  then  obtained  by  calculation.  The  drying 
is  carried  out  in  an  air-bath  or  steam  oven  at  constant  tempera- 
ture. The  determination  of  combined  water  will  be  described 
below. 

GENERAL  OUTLINE  OP  ANALYSIS 

After  the  preliminary  operations  above  described,  the  next 
step,  in  the  treatment  of  siliceous  material,  is  to  "open  up"  the 
substance  by  some  method  which  will  render  the  bases  soluble, 
and  the  whole  of  the  silica  insoluble,  in  dilute  acids.  Where 
conditions  allow,  this  is  done  by  fusion  in  platinum  vessels  with 
alkalis  or  alkaline  carbonates;  in  other  cases  the  sample  is  evap- 
orated or  boiled  with  nitric,  hydrochloric,  or  sulphuric  acid, 
according  to  circumstances.  In  the  filtrate  from  the  insoluble 
matter,  iron  and  alumina  are  generally  precipitated  together  by 
adding  excess  of  ammonia;  then,  successively,  the  group  con- 
taining manganese,  zinc,  nickel,  and  cobalt  by  ammonium  sul- 
phide, calcium  by  ammonium  oxalate,  and  magnesium  by  an 
alkaline  phosphate.  The  alkali  metals  are  estimated  in  a  sep- 
arate portion  of  the  sample.  In  cases  where  lead,  bismuth, 
arsenic,  antimony,  or  other  heavy  metals  capable  of  attacking 


ANALYSIS   OF  ORES   AND  SIMILAR  MATERIAL  397 

platinum  are  present,  these  must  be  eliminated  before  making 
any  fusions  in  platinum  vessels. 

ESTIMATION  OF  VARIOUS  INGREDIENTS 

ALKALI  METALS 

1.  These  are  generally  estimated  by  Lawrence  Smith's  method, 
as  follows:  A  weighed  portion,  say  1  gram,  of  the  finely  pow- 
dered ore  is  mixed  in  a  mortar  with  an  equal  weight  of  ammo- 
nium chloride,  then  with  eight  times  its  weight  of  pure  calcium 
carbonate,  and  transferred  to  a  platinum  crucible  provided  with 
a  funnel-shaped  prolongation  to  condense  any  alkaline  chloride 
which  may  be  volatilized  during  ignition.  The  crucible  is  heated, 
gently  at  first,  until  ammonium  salts  are  decomposed,  then  kept 
at  redness  for,  say,  three  quarters  of  an  hour.  When  cool  the 
contents  are  turned  into  a  dish  and  the  crucible  washed  into 
the  same  dish  with  water  (60  to  80  cc.)  and  boiled.  The  residue 
is  then  filtered,  the  filtrate  mixed  with  1.5  gram  ammonium 
carbonate  and  concentrated  somewhat;  then  more  ammonium 
carbonate  and  ammonia  are  added.  The  liquid  is  now  again 
filtered  into  a  weighed  platinum  dish,  evaporated  to  dryness, 
and  ignited  cautiously  to  below  redness.  When  cool  the  dish 
is  weighed,  the  increase  in  weight  giving  the  combined  chlorides 
of  the  alkali  metals.  The  residue  is  then  dissolved  in  water,  and 
the  chlorine  titrated  by  standard  silver  nitrate.  Deducting  the 
weight  of  chlorine  so  found  from  that  of  the  mixed  chlorides, 
we  have  the  total  weight  of  alkali  metals  present.  (For  separa- 
tion of  sodium  and  potassium  see  Potasskfm.) 

2.  In  cases  where  Lawrence  Smith's  method  is  inapplicable, 
as  when  the  sample  contains  large  quantities  of  the  heavy  metals, 
evaporate  to  dryness  with  aqua  regia,  ignite  to  render  silica 
insoluble,  take  up  with  dilute  hydrochloric  acid,  and  precipitate 
with  hydrogen  sulphide.  Treat  the  filtrate  with  ammonia  and 
ammonium  sulphide;  boil,  filter,  and  wash  with  dilute  ammonium 
sulphide.  Evaporate  the  filtrate  to  dryness  and  ignite  to  expel 
all  ammonium  chloride,  etc.  Re-dissolve  in  a  little  water,  add 
ammonium  carbonate  and  evaporate  to  dryness  on  a  water- 
bath.  Re-dissolve  in  warm  water  and  filter  into  platinum  dish. 
Evaporate  on  water-bath,  ignite  gently,  and  weigh  mixed  chlo- 
rides as  above. 


398  THE  CYANIDE  HANDBOOK 

ALUMINIUM 

This  metal  is  generally  precipitated  as  alumina,  together  with 
Fe,  Cr,  Ti,  Zr,  and  in  some  cases  phosphates  and  small  amounts 
of  Si02,  in  the  filtrate  from  the  silica.  After  determining  the 
total  weight  of  the  ignited  precipitate,  and  the  separate  amounts 
of  the  other  constituents,  the  alumina  (A12O3)  is  found  by  differ- 
ence. The  precipitation  is  made  either  by  ammonia  or  by 
sodium  acetate. 

1.  The  nitrate  from  silica  is  heated  nearly  to  boiling,  and 
ammonia  added  until  the  liquid  becomes  slightly  alkaline.     Suffi- 
cient ammonium  chloride  must  be  present  to  prevent  the  precip- 
itation of  magnesia,  etc.;  this  is  best  secured  by  acidulating  the 
liquid,  if  not  already  strongly  acid,  with  additional  hydrochloric 
acid  before   adding   ammonia.     After  stirring  and   allowing  to 
settle,  wash  by  decantation  with  hot  water  containing  a  little 
ammonia;  finally  transfer  to  a  filter,  allow  to  drain,  and  wash 
back  the  precipitate  into  the  original  dish.     Re-dissolve  in  hot 
dilute  HC1,  re-precipitate  with  ammonia  from  the  nearly  boiling 
liquid,  again  filter,  and  add  the  second  filtrate  to  the  first.     The 
precipitate  is  dried  carefully  in  an  air-bath,  removed  from  the 
papers,  which  should  be  burnt  separately,  ignited  over  an  oxidiz- 
ing blast  flame  in  a  platinum  crucible,  and  weighed  as  alumina, 
etc. 

2.  When  much  manganese  is  present,  it  is  better  to  precip- 
itate with  sodium  acetate,  as  follows:  The  acid  filtrate  from  the 
silica  is  nearly  neutralized  with  caustic  soda,  taking  care,  how- 
ever,  not  to   produce   a  permanent   precipitate.     From  2  to   3 
grams  of  sodium  acetate  are  then  added,  and  the  liquid  boiled, 
allowed  to  settle  somewhat,  filtered  and  washed  slightly.     The 
precipitate  is  re-dissolved  in  nitric  acid,  transferred  to  the  orig- 
inal vessel,  and  heated  nearly  to  boiling.     It  is  then  precipitated 
with  ammonia,  filtered,  and  washed  with  a  2  per  cent,  solution 
of  ammonium  nitrate,  care  being  taken  to  keep  the  two  filtrates 
separate.     By  concentrating  these  filtrates  separately,  an  addi- 
tional quantity  of  alumina,  etc.,  is  recovered.     The  first  filtrate 
is  then  re-filtered,  and  the  second  poured  on  to  the  same  filter, 
giving  a  final  wash  with  hot  dilute  ammonia.     The  united  fil- 
trate thus  obtained  serves  for  the  estimation  of  Mn,  etc.     The 
additional  precipitate  recovered  is  added  to  the  main  bulk,  dried 


ANALYSIS   OF   ORES   AND  SIMILAR  MATERIAL  399 

in  the  air-bath,   and  treated  as  already  described  in  the  first 
method. 

3.  The  nitrate  from  the  silica  is  oxidized  to  bring  all  iron  into 
the  ferric  state.  It  is  diluted  to  100  cc.  and  15  cc.  of  a  saturated 
solution  of  microcosmic  salt  (Na  •  NH4  •  HPO4  •  8H2O)  is  added, 
followed  by  ammonia,  till  a  slight  permanent  precipitate  remains. 
Heat  to  boiling;  acidulate  very  slightly  with  HC1,  add  25  cc. 
saturated  sodium  thiosulphate  and  5  cc.  glacial  acetic  acid;  boil 
for  10  minutes.  A  white  precipitate  is  formed  consisting  of 
aluminium  phosphate  mixed  with  sulphur.  Filter,  dry,  and  ig- 
nite with  the  paper;  finally  ignite  at  bright-red  heat  and  weigh 
as  A1PCV 

A12O3  X  0.5303  -  Al. 

A1PO4  X  0.4185  =  A12O3. 

A1PO4  X  0.2219  =  Al. 

ANTIMONY 

In  ores  containing  antimony,  this  metal  may  be  brought 
into  solution:  (1)  By  treatment  with  hydrochloric  acid  and  potas- 
sium chlorate.  (2)  By  fusion  with  an  alkali  and  sulphur.  The 
mass  extracted  with  water  contains  the  antimony  as  a  soluble 
sulphantimonite.  (3)  By  evaporation  with  sulphuric  and  tar- 
taric  acids,  the  latter  being  added  to  ensure  the  conversion  of 
antimony  into  an  antimonious  compound;  (4)  In  certain  ores, 
such  as  antimonite,  the  metal  may  be  dissolved  by  simply  boil- 
ing with  hydrochloric  acid. 

The  following  precautions  are  to  be  noted  in  manipulating 
solutions  containing  antimony:  (1)  The  chloride  is  very  liable 
to  precipitate  on  dilution,  as  SbOCL,;  this  may  be  prevented  by 
the  addition  of  a  little  tartaric  acid  before  precipitating  the  anti- 
mony, for  instance,  with  H2S.  (2)  Treatment  of  antimony  ores 
with  nitric  acid  forms  antimonic  acid,  which  is  soluble  with 
great  difficulty.  It  is  therefore  preferable  to  use  a  mixture  of 
HC1  and  KC103.  (3)  Antimonious  chloride,  SbCl3,  is  volatile 
on  evaporation;  solutions,  should  therefore  be  made  alkaline 
before  evaporating. 

Separation.  —  1.  Having  obtained  the  metals  in  HC1  solu- 
tion, the  liquid  is  mixed  with  excess  of  caustic  soda  and  a  little 
sulphur;  a  current  of  H2S  gas  is  passed  through  for  some  min- 

i  H.  T.  Waller,  Bull.  No.  49,  I.  M.  M.,  Oct.  8,  1908. 


400  THE  CYANIDE  HANDBOOK 

utes,  and  the  mixture  allowed  to  stand  in  a  warm  place  for  an 
hour;  it  is  then  filtered  and  washed,  the  Sb  being  in  the  filtrate 
as  sulphantimonite  (together  with  As  and  Sn  if  present).  Acid- 
ulate filtrate  with  HC1,  which  leaves  As2S3  undissolved  on  boil- 
ing. Filter,  dilute,  add  a  little  tartaric  acid;  re-precipitate  with 
H2S.  Filter  and  wash  free  from  chlorides.  Determine  Sb  as 
below. 

In  case  tin  also  is  present,  transfer  the  precipitate  to  a  weighed 
dish  and  treat  cautiously  with  fuming  nitric  acid.  Evaporate, 
ignite,  and  weigh  as  xSb2O4  +  ySnO2.  The  residue  in  the  dish 
is  then  transferred  to  a  flask  and  digested  for  an  hour  with  con- 
centrated tartaric  acid  solution,  on  a  water-bath,  avoiding  undue 
evaporation.  Residue  is  filtered,  washed,  ignited,  and  weighed 
as  ySn02.  The  precipitation  of  tin  by  H2S  may  be  prevented 
by  adding  a  sufficient  amount  of  concentrated  oxalic  -acid  solu- 
tion to  the  mixed  chlorides. 

2.  The  ore  is  heated  in  a  flask  with  a  mixture  of  tartaric  acid, 
sulphuric  acid,  and  potassium  bisulphate  until  completely  de- 
composed; all  carbon  separated  is  burnt  off  and  the  mixture 
heated  till  most  of  the  H2SO4  is  expelled.  Allow  to  cool  and 
dissolve  in  dilute  HC1  with  addition  of  tartaric  acid.  Heat  nearly 
to  boiling  and  pass  in  H2S.  Filter  and  wash  with  H2S  water. 
Transfer  the  precipitate  to  a  beaker  and  warm  with  potassium 
sulphide;  pass  again  through  same  filter,  washing  with  warm 
dilute  K2S.  The  Sb  (with  perhaps  As  and  Sn)  is  in  solution; 
convert  into  chlorides  by  repeating  the  original  treatment  with 
sulphuric  acid,  etc.,  finally  dissolving  in  strong  HC1.  Now  pass 
in  H2S,  which,  in  strongly  acid  solution,  precipitates  only  the 
As.  Filter,  wash  with  HC1,  dilute  filtrate  with  warm  water,  add 
oxalic  acid  if  tin  is  present,  and  precipitate  antimony  as  Sb2S3 
by  passing  H2S.  (For  details  see  A.  H.  Low,  "Technical  Methods 
of  Ore  Analysis,"  3d  edition,  pp.  32-35.) 

Estimation.  —  1.  The  antimony  is  assumed  to  have  been 
separated  as  antimonious  chloride,  SbCl3,  free  from  other  metals; 
add  excess  of  HC1,  boil  slightly  if  necessary  to  expel  SO2,  dilute 
considerably,  and  titrate  with  standard  permanganate  or  bi- 
chromate : 

5  SbCl3  +  2KMnO4  +  16HC1  =  5SbCls  +  2KC1  +  2MnCl2  +  8H2O 

V 
1  gram  KMnO4  =1.9  gram  Sb;  Ice.  ^  KMnO4  =  0.006  gram  Sb. 


ANALYSIS   OF   ORES   AND  SIMILAR  MATERIAL  401 

2.  When    the    antimony   has    been    obtained    as    antimonic 
chloride  (SbCl5),  as  in  the  case  where  the  ore  has  been  treated 
with  HC1  and  KC103,  the  excess  of  chlorine  is  boiled  off,  and  the 
solution  cooled,  diluted,  and  mixed  with  potassium  iodide. 

SbCl5  +  2KI  =  SbCl3  +  2KC1  +  I2. 
Ice.  TJJJ  iodine  <=  0.006  gram  Sb. 

After  standing  a  few  minutes,  the  liberated  iodine  is  titrated 
with  standard  thiosulphate.  The  thiosulphate  must  be  standard- 
ized against  a  known  quantity  of  antimony,  either  the  pure  metal 
dissolved  in  HC1  +  KC1O3  or  tartar  emetic,  also  heated  to  con- 
vert the  antimony  into  the  antimonic  condition. 

3.  Antimonious    compounds    may    also    be    titrated    with    a 
standard   solution  of  iodine  in   potassium  iodide,   as  described 
under  arsenic.1 

Detection.  —  The  presence  of  antimony  in  an  ore  may  often 
be  detected  by  heating  the  extract  obtained  with  hydrochloric 
acid  or  aqua  regia,  in  a  dish  containing  a  strip  of  platinum  in 
contact  with  metallic  zinc.  A  black  deposit  on  the  platinum, 
insoluble  in  dilute  HC1  but  soluble  in  HNO3,  indicates  antimony. 

ARSENIC 

Ores  containing  arsenic,  such  as  mispickel,  realgar,  orpiment, 
and  some  other  minerals,  are  occasionally  treated  by  cyanide; 
since  the  presence  of  arsenic  introduces  some  difficulties  in  the 
process,  attention  may  be  drawn  to  the  methods  of  detecting 
and  estimating  this  element. 

Dissolving.  —  1.  The  methods  already  described  for  anti- 
mony may  be  applied  in  general  for  arsenic. 

2.  Arsenic  may  be  obtained  in  the  arsenious  condition  by 
evaporating  the  powdered  ore  with  nitric  acid,  and  adding  the 
mixture  gradually  to  a  strong  solution  of  alkaline  sulphide,  warm- 
ing and  filtering,  the  arsenic  being  in  the  filtrate  as  sulpharsenite. 

3.  It  may  also  be  obtained  as  sulpharsenite  by  fusing  with 
sodium  carbonate  and  sulphur. 

4.  It  may  be  obtained  as  an  alkaline  arseniate  by  digesting 
the  ore  with  nitric  acid,  evaporating  to  dryness,  and  taking  up 
with  an  alkali. 

1  Sutton,  "Volumetric  Analysis,"  8th  edition,  p.  160. 


402  THE  CYANIDE  HANDBOOK 

5.  As  arseniate,  it  may  be  obtained  by  fusing  with  sodium 
carbonate  and  niter,  and  extracting  with  water. 

6.  By  suspending  the  finely  powdered  ore  in  a  caustic  alkali 
solution  and  passing  in  chlorine  till  saturated. 

7.  By  distilling  with  zinc  and  sulphuric  acid,  which  produce 
hydrogen   arsenide;    this   gas   when   led   through   fuming    nitric 
acid  forms  arsenic  acid. 

Separation.  —  1.  Having  obtained  the  arsenic  (together  with 
antimony  and  tin)  as  a  sulpharsenite,  the  insoluble  residue,  if 
any,  is  collected  on  a  filter  and  washed  with  dilute  potassium 
sulphide.  The  filtrate  is  acidulated  with  sulphuric  acid  and 
potassium  bisulphate,  adding  tartaric  acid  if  antimony  is  present. 
Heat  till  the  free  sulphur  and  most  of  the  acid  is  expelled,  then 
cool  and  add  strong  hydrochloric  acid.  Warm  gently  and  satu- 
rate with  H2S.  The  arsenic  is  precipitated  as  As2S3,  leaving  anti- 
mony and  tin  in  solution.  Filter  and  wash  with  HC1  (2:  I).1 

2.  In  cases  where  the  arsenic  has  been  converted  by  prelim- 
inary treatment  into  an  arsenious  compound,  it  may  be  separated 
from  other  (non-volatile)  ingredients  by  distillation  as  follows: 
The  substance  is  placed  in  a  flask  connected  with  a  bulbed  U- 
tube  or  other  suitable  condenser,  containing  a  little  water.  Add 
to  the  flask,  for  each  gram  of  material  treated,  30  grams  calcium 
chloride,  15  grams  ferric  chloride,  and  30  cc.  hydrochloric  acid. 
Distil  for  20  to  30  minutes  without  evaporating  to  dryness.  The 
arsenic  is  present  in  the  distillate  as  arsenious  chloride.  In  a 
modification  of  this  method,  ferrous  sulphate  is  used  instead  of 
ferric  chloride,  and  serves  to  reduce  any  arsenic  compound  that 
may  be  present. 

Estimation.  —  1.  Having  obtained  the  arsenic  as  an  arsen- 
ious compound  by  distillation  as  described  above,  or  by  dissol- 
ving the  sulphide  in  ammonium  sulphide  and  evaporating  with 
sulphuric  acid  and  potassium  bisulphate,  the  solution  is  made 
slightly  alkaline  with  ammonia,  then  slightly  acid  with  hydro- 
chloric acid.  When  cool,  a  sufficient  excess  of  sodium  bicar- 
bonate is  given,  and  the  mixture  titrated  with  standard  iodine 
and  starch  indicator.  The  iodine  solution  is  standardized  against 
known  quantities  of  arsenious  acid  (As2O3)  dissolved  in  hydro- 
chloric acid.2 

1  For  details  see  A.  H.  Low,  "Technical  Methods  of  Ore  Analysis,"  pp.  33-41. 

2  C.  and  J.  Beringer,  "Text  Book  of  Assaying,"  pp.  383-384. 


ANALYSIS   OF   ORES  AND   SIMILAR  MATERIAL  403 

N . 
1  cc.  r^  iodine  =  0.00375  gram  As. 

=  0.00495  gram  As2O3. 

2.  Gravimetric  Method.  —  When  the  arsenic  has  been  ob- 
tained as  an  arseniate,  the  mixture  is  made  alkaline  with  am- 
monia, and  a  mixture  of  magnesium  sulphate  and  ammonium 
chloride  added  (1  part  of  the  former  to  2  parts  of  the  latter). 
The  precipitate  is  allowed  to  settle,  filtered,  and  washed  with  a 
minimum  quantity  of  dilute  ammonia,  then  dried  very  slowly 
and  carefully  to  expel  ammonium  salts,  ignited,  and  weighed  as 
magnesium  pyroarseniate,  Mg2As2071. 

Mg2As2O7  X  0.4828  =  As. 

3.  Volumetric    Method,    for    Arseniates.  —  The    solution    is 
made  slightly  alkaline  with  ammonia,  then  mixed  with  sodium 
acetate  and  acetic  acid  till  distinctly  acid,  heated  to  boiling,  and 
at  once  titrated  with  standard  uranium   acetate,   using  ferro- 
cyanide  as  external  indicator;  the  appearance  of  a  brown  color 
in  the  spots  of  ferrocyanide  marks  the  end  of  the  titration.1 

4.  After  fusing  with  sodium  carbonate  and  niter  (5  parts  of 
each  to  1  part  of  the  ore),  dissolve  the  residue  in  warm  water, 
filter,  and  wash  with  cold  water.     Acidulate  slightly  with  nitric 
acid,  add  silver  nitrate,  then  successively  ammonia  and  nitric  acid, 
till    the    precipitate    just    dissolves    and    the    liquid    is   faintly 
acid.     Add  sodium  acetate  in  excess;  the  arsenic  is  precipitated 
as  silver  arsenate,  Ag3AsO4;  heat  to  boiling,  filter,  and  wash  with 
cold  water  till  "free  from  soluble  silver  salts,  re-dissolve  precip- 
itate with  dilute  nitric  acid,  and  estimate  the  silver  by  Volhard's 
method.     (See  p.  390.)     [Pearce's  method.]2 

N 
1  cc.  —  thiocyanate  =  0.0025  gram  As. 

Detection.  —  1.  The  substance  is  dissolved  in  hydrochloric 
acid,  or  the  arsenic  obtained  as  AsCL,  as  described  above.  A 
strip  of  copper  is  introduced  into  the  liquid,  which  is  then  warmed. 
Small  quantities  of  arsenic  give  a  gray  deposit,  and  larger  amounts 
a  black  deposit,  on  the  copper. 

2.  Marsh's  Test.  —  The  substance  to  be  examined  is  intro- 
duced into  a  vessel  containing  zinc  and  sulphuric  acid,  from 

1  C.  and  J.  Beringer,  loc  tit.,  p.  389. 

2  For  details,  see  A.  H.  Low,  "Technical  Methods  of  Ore  Analysis,"  3d  edi- 
tion, p.  42. 


404  THE   CYANIDE   HANDBOOK 

which  a  current  of  hydrogen  is  being  generated.  The  evolved 
gases  are  led  through  a  horizontal  tube  drawn  to  a  fine  point, 
forming  a  jet,  where  the  escaping  hydrogen  may  be  ignited.  By 
holding  a  cold  porcelain  plate  in  the  flame,  a  black  deposit  is 
obtained  consisting  of  reduced  metallic  arsenic  or  antimony; 
the  arsenic  deposit  may  be  distinguished  from  that  of  antimony 
by  its  greater  solubility  in  a  solution  of  a  hypochlorite.  A 
mirror  of  arsenic  may  also  be  obtained  by  heating  the  tube  at  a 
certain  point;  the  AsH3  is  decomposed  and  metallic  arsenic  depos- 
ited in  the  cooler  part  of  the  tube. 

3.  The  substance  is  mixed  with  dry  charcoal  and  heated  in  a 
bulb  tube.  A  sublimate  of  arsenic  is  formed,  and  when  much 
is  present  an  odor  resembling  garlic  is  observed. 

BARIUM 

When  the  ore  contains  the  metal  as  carbonate,  it  may  be 
extracted  by  simply  boiling  with  hydrochloric  acid.  In  other 
cases  the  ore  is  treated  successively  with  nitric  and  sulphuric 
acids  as  described  under  LEAD;  barium  and  strontium  remain  as 
sulphates,  together  with  silica,  in  the  portion  insoluble  in  ammo- 
nium acetate.  They  may  be  separated  from  silica  by  treating 
the  residue  in  a  platinum  crucible  with  H2SO4  and  HF.  In  the 
absence  of  lead,  however,  it  is  better  to  determine  barium  in  a 
separate  portion  of  the  sample;  this  is  treated  with  hydrofluoric 
and  sulphuric  acids,  and  evaporated  repeatedly  with  sulphuric 
acid  until  every  trace  of  fluorine  has  been  expelled.  The  evap- 
orated residue  is  digested  for  some  time  with  5  per  cent.  H2S04, 
boiled  if  necessary,  and  filtered.  The  filtrate  contains  any  other 
non-volatile  metals  which  may  have  been  present,  and  may  be 
used  for  their  estimation.  The  residue,  consisting  of  BaSO4 
and  SrS04,  with  perhaps  traces  of  CaS04,  is  ignited  with  sodium 
carbonate  and  extracted  with  water.  The  residual  carbonates 
are  then  dissolved  in  HC1.  If  strontium  be  present,  the  filtrate 
is  made  alkaline  with  ammonia,  a  slight  excess  of  acetic  acid  is 
added,  and  potassium  chromate,  which  precipitates  the  barium 
as  BaCrO4;  this  is  filtered,  washed  with  ammonium  acetate, 
ignited  gently  and  weighed. 

BaCrO4  X  0.542  =  Ba. 
Strontium  remains  in  the  filtrate,  and  may  be  precipitated  by 


ANALYSIS   OF   ORES   AND  SIMILAR  MATERIAL  405 

H2SO4.  When  no  strontium  is  present,  the  BaCO3  formed  by 
fusion  with  sodium  carbonate  is  at  once  dissolved  in  dilute  HC1, 
diluted,  heated  to  boiling,  and  precipitated  with  H2SO4.  After 
settling,  it  is  filtered,  washed  with  hot  water,  ignited,  and  weighed 
as  BaSO4.  BaSO4  x  0  5885  =  Ba 


If  any  calcium  should  be  present  in  this  precipitate  of  BaSO4, 
it  may  be  separated  by  dissolving  the  whole  in  concentrated 
H2SO4,  and  re-precipitating  the  BaSO4  by  dilution,  the  CaSO4 
remaining  dissolved. 

BISMUTH 

This  metal  is  obtained  together  with  copper  in  precipitating 
the  acid  extract  of  the  ore  with  H2S,  after  removal  of  lead,  etc., 
•  with  H2SO4,  as  described  under  copper.  In  order  to  separate  it, 
the  sulphide  precipitate  is  dissolved  in  nitric  acid  and  evaporated 
to  dryness,  taken  up  with  a  little  sulphuric  acid,  warmed  and 
filtered.  The  filtrate  is  nearly  neutralized  with  ammonia,  am- 
monium carbonate  added  in  excess,  boiled  and  filtered.  The 
precipitate  is  then  re-dissolved  in  HNO3,  and  re-precipitated 
from  boiling  solution  by  ammonium  carbonate,  filtered,  washed, 
dried,  ignited  at  low-red  heat,  and  weighed  as  Bi203. 

Bi2O3  X  0.8966  =  Bi. 

CADMIUM 

This  metal  is  precipitated  by  H2S  with  copper  and  bismuth. 
It  remains  in  solution  together  with  copper  when  the  bismuth  is 
precipitated  as  carbonate  in  ammoniacal  solution.  Cadmium 
may  be  detected  and  estimated  by  adding  cyanide  to  the  blue 
ammoniacal  liquor  till  it  is  colorless,  then  passing  in  H2S,  which 
gives  a  yellow  precipitate,  leaving  the  copper  in  solution.  The 
precipitate  is  collected  on  a  weighed  filter,  washed  with  sulphu- 
reted  hydrogen  water,  then  extracted  with  carbon  bisulphide 
to  remove  free  sulphur,  dried  at  100°  C.  and  weighed  as  CdS. 

CdS  x  0.7781  =  Cd. 

CALCIUM 

Separation.  —  1  .  Calcium  is  generally  determined  in  the  filtrate 
from  the  group  containing  zinc  and  manganese;  this  filtrate  is 
boiled  to  expel  excess  of  ammonium  sulphide,  filtered  if  not  quite 


406  THE  CYANIDE  HANDBOOK 

clear,  then  mixed  with  a  boiling  solution  of  ammonium  oxalate. 
After  settling  clear,  the  precipitate  is  filtered  off  and  washed 
with  hot  water.  In  cases  where  much  calcium  is  present  the 
precipitate  is  re-dissolved  in  a  minimum  quantity  of  HC1  and 
re-precipitated  from  boiling  solution  with  ammonia  and  ammo- 
nium oxalate.  This  double  precipitation  is  necessary  because 
calcium  oxalate  retains  both  magnesium  and  sodium  salts  very 
tenaciously. 

2.  A  direct  separation  in  the  filtrate  from  silica  may  be  made 
as  follows.  The  liquid  is  heated  nearly  to  boiling,  excess  of  am- 
monia added,  then  solid  oxalic  acid  till  iron  is  dissolved.  Neu- 
tralize exactly  with  ammonia  and  add  oxalic  acid  until  the  ferric 
hydrate  just  dissolves.  On  boiling,  the  calcium  is  precipitated 
as  oxalate,  free  from  iron.  In  presence  of  manganese  it  may 
be  necessary  to  add  bromine  water  after  the  first  addition  of 
ammonia;  boil,  filter,  and  wash  with  hot  water  before  proceeding 
to  add  oxalic  acid. 

Estimation.  —  1  .  When  calcium  has  been  precipitated  as  oxa- 
late it  may  be  conveniently  and  accurately  estimated  by  titra- 
tion  with  standard  permanganate.  The  precipitate  is  washed 
thoroughly  with  hot  water,  dissolved  in  dilute  sulphuric  acid, 
heated  to  70°  C.,  and  titrated  with  permanganate  till  the  pink 
tint  remains  permanent.  The  permanganate  should  be  standard- 
ized on  pure  crystallized  oxalic  acid. 

1  part  oxalic  acid  (C2H2O4  •  2H2O)  =  0.4451  parts  CaO. 

Special  methods  for  determining  the  percentage  of  caustic 
lime  in  commercial  samples  will  be  described  in  a  later  section. 

Ice.  ^  KMnO4  =  0.0028  gram  CaO. 

=  0.0020  gram  Ca. 

A  convenient  standard  solution  is  one  containing  1.58  gram 
KMn04  per  liter,  so  that 

1  cc.  =  0.001  gram  Ca. 
The  reactions  are  as  follows: 

Ca(C2O4)  +  H2SO4  =  CaSO4  +  H2C2O4. 
2KMnO4  +  5H2C2O4  +  SHzSO*  =  K2SO4  +  2MnSO4  +  10CO2  +  8H2O 


2.  Calcium  may  also  be  determined  gravimetrically  by  strong 
ignition  of  the  precipitate,  and  weighing  as  lime,  CaO,  or  by 
gentle  ignition,  afterwards  moistening  the  residue  with  ammo- 


ANALYSIS   OF   ORES   AND  SIMILAR  MATERIAL  407 

nium  carbonate,  evaporating  to  dryness,  heating  just  to  redness, 
and  weighing  as  calcium  carbonate,  CaCO3. 

CaCO3  X  0.4006  =  Ca. 
CaCO3  X  0.5604  =  CaO. 

CARBONIC    ACID 

The  carbonic  acid  in  ores  exists  in  the  form  of  carbonates, 
generally  insoluble  in  water  but  soluble  in  dilute  acids.  It  may 
be  estimated  in  one  or  other  of  the  numerous  types  of  carbonic 
acid  apparatus,  of  which  the  general  principle  is  as  follows:  The 
apparatus  is  weighed,  first  without  and  afterwards  with  the  por- 
tion of  ore  to  be  analyzed.  The  dilute  acid  (HNO3  or  HC1)  which 
serves  to  decompose  the  carbonate  is  then  allowed  to  come  in 
contact  with  the  ore  by  turning  the  tap  of  the  bulb  in  which  it 
is  contained  and  momentarily  opening  the  stopper.  The  escaping 
gas  has  to  pass  through  a  bulb  containing  sulphuric  acid, 
which  retains  any  moisture.  Gentle  heat  is  necessary  in  some 
cases  for  complete  expulsion  of  carbonic  acid.  When  the  action 
is  complete,  a  slow  current  of  air  is  aspirated  through  the  appa- 
ratus, which  is  then  again  closed  and  weighed,  the  loss  of  weight 
giving  the  CO2  expelled. 

3.  For  more  exact  determinations  the  gas  is  passed  through 
a  series  of  tubes  containing  desiccating  agents,  such  as  strong 
sulphuric  acid,  anhydrous  copper  sulphate,  calcium  chloride, 
etc.,  and  the  C02  is  absorbed  by  soda-lime  contained  in  a  weighed 
U-tube.  The  inlet  of  the  flask  in  which  the  decomposition  of 
the  carbonate  takes  place  is  protected  by  a  U-tube  of  soda  lime 
to  absorb  any  atmospheric  CO2  which  might  otherwise  enter  the 
apparatus,  and  the  exit  end  of  the  weighed  tube  is  protected  by 
a  U-tube  containing  a  desiccating  agent  and  absorbent  of  CO2. 
Air  is  then  aspirated  through  the  whole  apparatus,  and  the 
weighed  U-tube  detached,  closed,  and  weighed.  The  increase 
of  weight  gives  the  CO2. 

CHLORINE 

Chlorine  occurs  as  chlorides  in  small  quantities  in  certain  ores. 
Silver  occurs  occasionally  as  "horn-silver"  (AgCl),  in  which  form 
it  is  readily  extracted  by  cyanide.  When  insoluble  chlorides 
are  present,  the  crushed  ore  is  fused  with  sodium  carbonate  and 
chlorine  determined  in  the  aqueous  extract.  Any  heavy  metals 


408  THE  CYANIDE  HANDBOOK 

present  in  the  extract  are  removed  by  H2S,  the  excess  of  which 
must  be  boiled  off.  The  liquid  is  then  made  acid  with  HNO3 
and  the  chlorine  determined. 

Estimation.  —  1 .  If  present  in  sufficient  quantity,  it  may  be 
titrated  in  neutral  solution  by  AgNO3,  with  potassium  chromate 
(K2CrO4)  as  indicator.  The  silver  solution  is  added  till  a  per- 
manent reddish  tint  remains  after  agitation.1 

2.  In  cases  where  it  is  inconvenient  to  neutralize  the  solu- 
tion,  a  measured   amount  of  standard  silver  nitrate  is  added, 
more  than  sufficient  to  precipitate  the  chlorine,  and  the  liquid 
acidified  with  HNO3.     The  AgCl  is  then  filtered  off  and  the  resid- 
ual AgNO3  determined  by  titrating  with  standard  potassium  or 
ammonium  thiocyanate,  using  ferric  nitrate  or  sulphate  as  in- 
dicator.2 

3.  Very  small  quantities  are  best  estimated  gravimetrically 
as  AgCl.     The  liquid,  which  must  be  slightly  acid  with  HNO3, 
is  mixed  with  a  few  drops   of  AgNO3,   boiled   thoroughly,  and 
allowed  to  stand  for  some  time.     The  AgCl  should  settle  in  a 
dense  form.     It  is  then  washed  by  decantation,  without  filtering, 
transferred  to  a  weighed  porcelain  crucible,  dried  and  heated  to 
incipient  fusion,  cooled,  and  weighed  as  AgCl. 

AgCl  X  0.2472  =  Cl. 

CHROMIUM 

This  metal  occurs  as  chrome  iron  ore;  it  is  precipitated  along 
with  Al  and  Fe  in  treating  the  filtrate  from  silica  with  ammonia 
or  with  sodium  acetate.  It  is  preferable,  however,  to  determine 
it  in  a  separate  portion  of  the  ore.  This  must  be  ground 
extremely  fine  and  fused,  either  with  sodium  carbonate  and  niter, 
or  with  sodium  peroxide,  to  convert  the  chromium  into  a  soluble 
yellow  chromate.  The  metal  is  dissolved  in  water,  giving  a  yel- 
low solution. 

Determination.  —  1.  When  only  small  quantities  are  present, 
the  chromium  may  be  determined  colorimetrically  by  compari- 
son with  a  standard  solution  of  K2CrO4. 

2.  If  present  in  larger  amount,  the  solution,  after  boiling  off 
any  excess  of  sodium  peroxide,  is  mixed  with  ammonium  carbo- 
nate to  partially  neutralize  the  caustic  alkali,  filtered,  and  acidified 

1  For  details,  see  Sutton,  "Volumetric  Analysis,"  p..  152  (8th  edition). 

2  Sutton,  loc.  tit.,  pp.  155,  184. 


ANALYSIS   OF   ORES  AND  SIMILAR  MATERIAL  409 

with  dilute  sulphuric  acid.  An  excess  of  ferrous  ammonium 
sulphate  is  then  given,  by  adding  a  weighed  quantity  of  the 
salt,  and  the  residual  ferrous  iron  titrated  with  permanganate. 

1  cart  Fe  =  0.3107  parts  Cr. 
COBALT 

The  sample  is  evaporated  to  dryness  with  HNO3  and  KC1O3. 
The  residue  is  dissolved  in  dilute  HC1,  heated  to  boiling,  and  pre- 
cipitated with  H2S.  The  nitrate  from  H2S  precipitate  is  boiled 
to  expel  excess  of  H2S,  a  few  drops  of  HNO3  added,  and  the  iron 
precipitated  by  ammonia.  The  filtrate  is  then  made  strongly 
acid  with  acetic  acid,  adding  ammonium  acetate  and  heating  to 
about  70°  C.  On  again  passing  in  H2S,  cobalt,  nickel,  and  zinc 
are  precipitated,  leaving  manganese  in  solution.  Filter,  wash 
with  warm  water,  and  re-dissolve  the  precipitate  in  HC1  +  HNO3. 
Add  a  considerable  excess  of  ammonium  chloride,  evaporate  to 
dryness,  and  ignite  to  volatilize  zinc  chloride;  re-dissolve  the 
residue,  which  now  contains  only  Co  and  Ni,  in  HC1  +  HNO3. 

Determination  of  Cobalt.  —  The  extract  containing  Co  and 
Ni  is  made  alkaline  with  caustic  alkali,  acidified  with  acetic 
acid,  and  mixed  with  a  concentrated  solution  of  potassium  ni- 
trite. On  standing  in  a  warm  place  (best  for  24  hours)  the  cobalt 
separates  as  a  yellow  precipitate  (dauble  nitrite  of  cobalt  and 
potassium).  This  is  filtered  off,  washed  with  potassium  acetate 
solution  and  finally  with  alcohol,  dried,  heated  in  a  porcelain 
crucible  with  sulphuric  acid,  ignited  at  a  very  low  red  heat  and 
weighed  as  2  CoSO4  +  3  K2SO4. 

Weight  of  residue  X  0.1416  =  Co. 

COPPER 

The  presence  of  copper  in  ores  to  be  treated  by  cyanide  intro- 
duces such  difficulties  that  the  detection  and  estimation  of  the 
metal  may  become  a  matter  of  considerable  importance. 

Detection.  —  In  most  cases  the  presence  of  copper  is  readily 
detected  by  boiling  a  small  quantity  of  the  ore  in  strong  nitric 
acid,  diluting  and  neutralizing  the  acid  with  ammonia.  On 
allowing  to  settle,  the  presence  of  copper  is  shown  by  a  blue  color 
in  the  supernatant  liquid.  It  may  be  confirmed  by  filtering  a 
little  of  the  fluid,  rendering  just  acid  with  hydrochloric  or  acetic 


410  THE  CYANIDE  HANDBOOK 

acid  and  adding  a  drop  of  ferrocyanide  solution,  which  gives  a 
reddish-brown  coloration.  In  order  to  determine  whether  the 
copper  in  an  ore  is  in  a  form  readily  attacked  by  cyanide,  a  little 
of  the  crushed  ore  may  be  shaken  with  cyanide  solution  and 
filtered;  if  the  filtrate  be  acidulated  and  a  drop  of  ferrocyanide 
added,  the  characteristic  reddish-brown  color  is  obtained  if  any 
copper  has  been  dissolved. 

Separation.  —  1 .  In  cases  where  lead  has  also  to  be  determined, 
the  copper  may  be  estimated  in  the  filtrate  from  the  lead 
sulphate  precipitate,  after  the  alcohol  has  been  boiled  off.  It 
may  be  precipitated  as  sulphide,  best  from  a  hot  solution,  by 
sulphureted  hydrogen  or  by  sodium  thiosulphate,  or  it  may 
be  precipitated  on  aluminium  as  described  below,  in  the  form 
of  finely  divided  metallic  copper. 

2.  A  portion  of  the  crushed  ore  (0.5  gram  to  2  or  3  grams, 
according  to  richness  in  copper)  is  evaporated  nearly  to  dryness 
with  HN03.     It  is  then  boiled  with  HC1  and  finally  with  H2SO4, 
heating  till  white  fumes  are  freely  evolved.     Cool,  dilute,  and 
filter.     Wash  with  hot  water.     The  copper  in  the  filtrate  is  now 
precipitated  as  sulphide  by  passing  a  current  of  H2S  gas  through 
the  nearly  boiling  liquid;  when  saturated,  allow  to  settle  for  a  few 
minutes,  filter  while  still  hot,   and  wash  with  H2S  water.     In 
presence  of  much  iron,  the  sulphide  precipitate  must  be  re-dis- 
solved in  HNO3,  again  boiled  with  H2S04,  diluted  and  re-precip- 
itated with  H2S.     Dissolve  the  precipitate  in  concentrated  HNO3, 
adding  a  little  potassium  chlorate  if  arsenic  or  antimony  is  pres- 
ent; boil  thoroughly,  filter  off  any  undissolved  sulphur.     If  any 
undissolved    precipitate    remains   on   the    filter-paper,    dry    and 
ignite  the  latter,  dissolve  the  ash  in  boiling  HNO3,  and  add  to  the 
bulk  of  the  solution.     The  copper  is  in  solution  as  nitrate,  with 
perhaps  Bi,  Cd,  or  some  other  metals.     In  presence  of  Bi,  add 
excess  of  ammonia,  boil  and  filter. 

3.  Proceed  as  in  method  No.  2,  until  white  fumes  are  given 
off  on  heating  with  H2SO4.     Then  cool,  dilute  and  heat  to  boiling. 
Filter  off  any  precipitate  of  PbSO4,  etc.     Wash  with  hot  water, 
dilute  to  (say)  75  cc.,  add  one  or  more  sheets  of  aluminium,  bent 
so  as  not  to  lie  flat  in  the  beaker.     Boil  about  ten  minutes,  till 
the  copper  is  precipitated  in  a  spongy  form.     Decant  the  liquid 
through  a  filter,  and  wash  the  copper  on  to  the  filter  with  H2S 
water  till  all  iron,  etc.,  is  removed.     The  copper  adhering  to  the 


ANALYSIS   OF   ORES   AND  SIMILAR  MATERIAL  411 

aluminium  is  then  dissolved  in  hot  50  per  cent,  nitric  acid,  which 
is  afterwards  poured  over  the  precipitate  in  the  funnel,  together 
with  a  little  bromine  or  KC1O3;  collect  the  filtrate  in  a  flask,  wash 
with  hot  water,  boil  thoroughly  to  expel  Br  or  Cl,  and  add  am- 
monia. 

4.  Certain  slags  contain  all  or  nearly  all  the  silica  in  a  form 
soluble  in  HC1,  the  copper  being  present  as  sulphide,  insoluble 
in  that  acid.  In  such  cases  the  sample  is  simply  treated  with 
hot  dilute  HC1  and  filtered.  Dry,  ignite,  and  treat  the  residue 
with  HNO3  and  a  little  HC1.  Boil  off  red  fumes,  dilute,  add  am- 
monia, boil,  and  filter. 

Estimation.  —  1.  If  the  copper  has  been  obtained  in  nitric 
acid  solution,  neutralize  with  sodium  carbonate,  and  add  ammonia 
till  a  clear-blue  solution  is  obtained.  Filter  if  necessary  (e.g., 
if  Bi  is  present).  If  the  copper  contents  are  approximately 
known,  prepare  a  similar  solution  containing  about  the  same 
amounts  of  copper,  nitric  acid,  and  ammonia,  using  pure  copper 
foil.  This  solution  is  used  as  a  standard.  Titrate  the  blue  solu- 
tions as  nearly  as  possible  at  the  same  time  with  a  solution  of 
potassium  cyanide  0.5  to  2  per  cent.  KCN,  according  to  circum- 
stances, running  in  the  solution  until  a  faint  violet  color  of  equal 
intensity  remains  in  each.  When  approaching  the  finish,  the 
cyanide  solution  should  be  run  in  a  little  at  a  time,  in  quantities 
of  say  0.5  cc.,  waiting  some  time  before  making  a  fresh  addition, 
as  the  reaction  takes  place  slowly. 

2.  The  nitric  acid  solution  of  the  copper  is  neutralized  with 
sodium  carbonate,  and  acetic  acid  added  until  the  precipitate 
dissolves.  (Ammonia  may  be  used  instead  of  sodium  carbon- 
ate.) Cool,  and  add  about  10  parts  of  potassium  iodide  for  every 
part  of  copper  supposed  to  be  present.  The  following  reaction 
takes  place: 

2Cu(CH3CO2)2  +  4KI  =  Cu2I2  +  I2  +  4  (KCH3CO2). 

The  liberated  iodine  is  then  titrated  at  once  with  standard 
sodium  thiosulphate,  adding  starch  solution  towards  the  finish.1 

Ice.  —  thiosulphate  =  0.0063  gram  Cu. 

In  this  process  care  must  be  taken  that  no  iron  or  nitrous 
acid  are  present,  and  the  liquid  must  not  be  too  dilute;  if  these 

1  Sutton,  loc.  tit.,  p.  201.      Beringer,  loc.  cit.,  p.  199. 


412  THE  CYANIDE  HANDBOOK 

conditions  are  neglected,  the  blue  color  of  the  iodine  returns 
on  standing  for  a  few  moments  and  no  definite  end-point  can  be 
obtained.  Bismuth  interferes  with  the  process,  as  it  gives  a 
color  with  iodine;  if  present,  it  may  be  separated  by  boiling  the 
solution  with  carbonate  of  ammonium  and  filtering,  before  add- 
ing the  acetic  acid. 

3.  When  only  small  quantities  of  copper  are  present,  they 
may  be  determined  colorimetrically,  by  comparing  the  tint  of 
the  ammoniacal  solution  with  that  of  a  liquid  in  a  similar  vessel 
containing  amounts  of  nitric  acid  and  ammonia  approximately 
corresponding  to   those   in  the   assay,    adding   standard   copper 
nitrate  until  the  colors  are  alike.     Still  smaller  quantities  may  be 
determined   colorimetrically   by   using   a   standard   ferrocyanide 
solution. 

4.  The  copper  is  obtained  in  slightly  acid  HC1  solution,  and 
is  reduced  by  sodium  sulphite  and  precipitated  with  thiocyanate. 
The   cuprous  thiocyanate  is  then   boiled,   filtered,   and  washed 
thoroughly  with  hot  water.      It  is  next  dissolved  off  the  filter 
with  boiling  caustic  soda,  and  the  resulting  sodium  thiocyanate 
titrated  with  permanganate  after  acidulating  with    H2SO4.     The 
permanganate  solution  should   be  standardized  on  pure  copper 
under  the  conditions  of  the   assay,   as   cuprous  thiocyanate  is 
slightly  soluble  in  the  reagents  used. 

5.  The  writer  has  found  that  small  amounts  of  copper  may 
be  readily  and  accurately  estimated  by  a  method  nearly  iden- 
tical in  principle  with  that  of  T.  Moore  for  the  estimation  of  nickel.1 
(See  below.)     The  copper  is  obtained  in   a  nitrate  or  sulphate 
solution  free  from  other  metals.     Sufficient  caustic  soda  is  added 
to  precipitate  the  whole  of  the  copper,  avoiding  a  large  excess  of 
alkali;   then   standard   cyanide   solution,   in   measured   amount, 
until  a  perfectly  colorless  liquid  is  obtained.     Potassium  iodide 
is  then   added   and  the  excess   of   cyanide  titrated  with  silver 
nitrate.     The  presence  of  ammonia  or  ammonium  salts  vitiates 
the  test.     A  constant  excess  of  cyanide  should  be  used  in  all 
cases,  as  the  amount  of  copper  indicated  increases  slightly  with 
increased  excess  of  cyanide.     Satisfactory  results  were  obtained 
with  solutions  containing  from   1   to   50  mg.   Cu.     The  results 
were  on  a  par  with  the  iodide  method  in  point  of  accuracy,  and 
superior  to  the  ordinary  cyanide  method. 

i  "Chem.  News,"  LXXII,  92. 


ANALYSIS   OF   ORES  AND  SIMILAR  MATERIAL  413 

FLUORINE 

Fluorine  occurs  in  ores  chiefly  as  fluor-spar  (CaF2)  and  as 
cryolite  (Na3AlF6).  It  may  be  determined l  by  mixing  the 
finely-ground  ore  with  an  .excess  of  powdered  silica  and  dis- 
tilling with  concentrated  sulphuric  acid  for  two  hours  at  a  gentle 
heat,  whereby  the  fluorine  is  expelled  as  gaseous  silicon  fluoride : 

2CaF2  +  2H2SO4  +  SiO2  =  2CaSO4  +  2H2O  +  SiF4. 

During  the  distillation  a  current  of  air  is  made  to  pass  slowly 
through  the  apparatus,  and  the  silicon  fluoride,  which  should  be 
cooled  by  leading  through  a  bulb-tube  immersed  in  water,  is 
passed  into  an  alcoholic  solution  of  potassium  chloride  (30  parts 
KC1  in  100  parts  alcohol  and  100  water),  by  which  it  is  decom- 
posed as  follows: 

3SiF4  +  2H2O  +  4KC1  =  SiO2  +  2K2SiF6  +  4HC1. 

The  potassium  silicofluoride  remains  undissolved  in  the  alcoholic 
solution.  By  titrating  the  HC1  with  standard  alkali  and  lac- 
moid  indicator,  the  amount  of  fluorine  may  be  determined. 

1  equivalent  HC1  =  3  equivalents  F. 
Ice.  ~  HC1  =  0.0057  gram  F. 

IRON 

Separation.  —  The  estimation  of  iron  is  generally  made  in 
the  filtrate  after  separation  of  silica.  The  methods  of  separation 
with  ammonia  and  with  sodium  acetate  are  described  under 
aluminium.  In  a  few  cases  the  precipitate  of  alumina,  etc., 
formed  under  these  circumstances,  can  be  ignited  and  weighed, 
and  afterwards  completely  dissolved  by  boiling  with  concen- 
trated sulphuric  acid.  In  general,  however,  the  ferric  oxide, 
after  ignition,  resists  the  action  of  acids  very  strongly  and  can 
only  be  got  completely  into  solution  by  long-continued  fusion 
(2  to  4  hours)  with  potassium  bisulphate.  The  fusion  should  be 
conducted  at  as  low  a  temperature  as  possible,  and  the  bisul- 
phate should  have  been  previously  fused  by  itself,  to  expel  water- 
vapor  and  excess  of  acid.  The  molten  mass  is  allowed  to  cool, 
dissolved  in  water  to  which  a  little  sulphuric  acid  is  added,  boiled 
and  filtered.  Any  residual  silica  is  here  collected  and  estimated. 

i  Penfield,  "Chemical  Engineer,"  III,  65. 


414  THE  CYANIDE  HANDBOOK 

Estimation.  —  1.  Trie  liquid  obtained  as  above  is  treated 
with  a  reducing  agent,  cooled  and  titrated  with  permanganate. 
The  reduction  may  be  carried  out  in  many  ways.  The  writer 
prefers  boiling  with  clean  aluminium  turnings  until  a  drop  of 
the  liquid  no  longer  reacts  with  a  drop  of  thiocyanate  solution. 
Other  methods  of  reduction  commonly  employed  are  with  zinc, 
with  sulphureted  hydrogen,  and  with  sodium  sulphite.1  Care 
must  be  taken  to  avoid  oxidation  of  the  iron  in  the  solution  dur- 
ing the  cooling  process.  When  much  iron  is  present,  it  may  be 
necessary  to  dilute  with  boiled,  cooled,  distilled  water  before 
titrating  with  permanganate.  The  permanganate  solution  is 
standardized  on  pure  iron  wire  dissolved  in  pure  20  per  cent, 
sulphuric  acid,  or  on  a  known  weight  of  pure  dry  ferrous  ammo- 
nium sulphate,  FeSO4(NH4)2SO4  •  6H2O. 

2.  The  liquid,  reduced  in  the  manner  described,  or   (more 
rapidly)  by  addition  of  a  small  excess  of  stannous  chloride  — 
which   excess   is   afterwards   removed   by   cautious   addition   of 
mercuric  chloride  —  is  titrated  with  a  standard  solution  of  potas- 
sium bichromate,  using  ferricyanide  of  potassium,  in  spots  on  a 
white  porcelain  plate,  as  external  indicator.     For  the  estimation 
of  iron  in  slags,  0.5  grams  of  the  sample  may  be  dissolved  in  25 
cc.  boiling  water,  with  addition  of  20  cc.  HC1.     The  mixture  is 
stirred  vigorously  and  boiled  to  expel  H2S.     Then  add  SnCl2  in 
slight  excess,  cool,  and  add  20  cc.  of  a  saturated  solution  of  mer- 
curic chloride.     Titrate  with  bichromate  solution,  4.392  grams 
K2Cr2O7  per  liter.2 

3.  Very  small  amounts  of  iron  are  best  estimated  by  the 
colorimetric  method.     The  ferric  hydrate  or  basic  acetate  pre- 
cipitate is  dissolved  in  HC1,  a  sufficient  excess  of  thiocyanate 
solution  added,  and  the  tint  compared  with  that  produced  under 
similar   conditions   by   measured    quantities   of   standard    ferric 
chloride  solution,  using  the  same  amount  of  thiocyanate  in  each 
case.     The  standard  solutions  may  be  conveniently  adjusted  so 
that  1  cc.  =  0.01  or  0.001  gram  Fe,  according  to  the  amount  to 
be  estimated. 

LEAD 

Separation.  —  In  some  ores,  such  as  pure  galena,  the  lead 
may  be  completely  extracted  by  boiling  with  strong  hydrochloric 

1  C.  and  J.  Beringer,  Text  Book  of  Assaying,  9th  edition,  p.  235. 

2  H.  T.  Waller,  Bull.  I.  M.  M.,  No.  49,  Oct.  8,  1908. 


ANALYSIS   OF   ORES   AND   SIMILAR  MATERIAL  415 

acid;  in  other  cases  nitric  acid  is  used,  with  addition  of  a  few 
drops  of  HC1.  After  boiling  for  some  time,  the  flask  is  allowed 
to  cool,  and  sufficient  sulphuric  acid  added  to  precipitate  the 
whole  of  the  lead  as  PbSO4,  together  with  barium  and  perhaps 
some  other  metals.  Evaporate  until  dense  white  fumes  of  sul- 
phur trioxide  are  given  off.  Cool,  dilute  carefully,  and  boil. 
Again  cool,  add  alcohol,  stir  and  settle  thoroughly  (over  night 
if  possible).  Decant  the  clear  liquid  and  wash  by  decantation 
with  dilute  sulphuric  acid  containing  about  10  per  cent,  of  alco- 
hol, finally  with  pure  alcohol,  leaving  the  residue  as  much  as 
possible  in  the  beaker.  The  filtrate  may  serve  for  the  estima- 
tion of  copper,  etc.  To  the  residue  add  a  strong  solution  of 
ammonium  acetate,  with  a  slight  excess  of  acetic  acid,  to  dis- 
solve PbSO4,  leaving  Si02,  BaS04,  CaSO4,  etc.,  undissolved. 
Moisten  the  filter  with  ammonia  and  pass  the  liquid  through 
into  a  clean  flask  or  beaker.  Wash  first  with  dilute  ammonium 
acetate,  then  with  hot  water. 

Estimation.  —  1.  Gravimetric  Method.  Acidulate  the  fil- 
trate, obtained  as  above,  with  sulphuric  acid.  Allow  to  settle 
for  some  time  and  filter.  The  precipitate  is  separated  as  much 
as  possible  from  the  paper,  ignited  carefully,  and  the  ash  of  the 
paper,  separately  ignited  and  treated  successively  with  HNO3  and 
H2SO4,  is  added.  Weigh  as  PbSO4.  .  It  is  preferable  to  collect 
the  final  precipitate  of  PbSO4  on  a  weighed  perforated  porcelain 
crucible  with  asbestos  filter.  This  is  washed  with  absolute  alco- 
hol, dried,  ignited,  and  again  weighed. 

PbSO4  X  0.6829  =  Pb. 

2.  Several  volumetric  methods  are  in  use,1  which  are  appli- 
cable where  the  quantity  of  lead  is  considerable,  (a)  The  lead 
sulphate  is  dissolved  in  ammonium  acetate,  and  titrated  in  hot 
solution  with  standard  ammonium  molybdate,  using  tannin  as 
indicator,  which  gives  a  brown  tint  with  excess  of  molybdate. 
A  correction  is  required  for  the  amount  of  molybdate  solution 
necessary  to  develop  this  color.  (6)  Chromate  of  potassium  is 
added  in  excess;  the  excess  is  then  determined  either  colorimet- 
rically  or  by  means  of  a  ferrous  iron  solution,  (c)  The  lead  dis- 
solved as  acetate  is  titrated  with  standard  ferrocyanide  at  about 
60°  C.,  using  uranium  acetate  as  indicator. 

1  See  Beringer,  loc.  tit.;  also  Irving  C.  Bull.  "Sch.  of  Mines  Qly.,"  XXIII,  No. 
4;  "Chem.  News,"  LXXXVII,  40. 


416  THE  CYANIDE  HANDBOOK 

MAGNESIUM 

1.  After  precipitation  of  calcium  as  oxalate,  the  nitrate  is 
made  strongly  alkaline  with  ammonia,  and  mixed  with  an  excess 
of  sodium  or  ammonium  phosphate,  well  stirred  without  touch- 
ing the  sides  of  the  vessel  with  the  stirring-rod,  and  allowed  to 
settle  for  a  considerable  time  (2  or  3  hours).     The  precipitate  is 
then  filtered  off  and  washed  with  2.5  per  cent,   ammonia.     In 
exact  analysis  it  should  be  re-dissolved  in  HC1  and  re-precip- 
itated  with   ammonia   and   phosphate.     In   washing,   the   mini- 
mum necessary  amount  of  wash-water  should  be  used,  and  the 
first  portions  of  the  precipitate  are  best  washed  on  to  the  filter, 
by  means  of  a  small  quantity  of  the  filtrate.     When  free  from 
chlorides,  the  precipitate  is  dried,  ignited,  moistened  with  nitric 
acid,  cautiously  evaporated  to  dryness,  then  again  ignited  and 
weighed  as  magnesium  pyro phosphate  (Mg2P2O7). 

Mg2P2O7  X  0.2188  =  Mg. 

2.  Magnesium  may  also  be  estimated  volumetrically  by  dis- 
solving the  precipitate  of  magnesium  ammonium  phosphate  in 
decinormal  sulphuric  acid  and  titrating  the  excess  of  acid  with 
standard  alkali  and  methyl  orange.1 

Ice.  —  H2SO4  =  0.001218  gram  Mg. 

=  0.002018  gram  MgO. 

MANGANESE 

Separation.  —  1.  Manganese  is  contained  in  the  filtrate 
obtained  after  precipitating  iron,  alumina,  etc.,  with  ammonia 
or  with  sodium  acetate.  Its  presence  is  generally  indicated  at  an 
earlier  stage  by  the  greenish,  sometimes  purplish,  color  of  the 
melt  obtained  with  the  ore  and  sodium  carbonate;  this  color 
disappears  on  treatment  with  hydrochloric  acid.  Manganese 
may  be  precipitated,  along  with  some  other  metals,  by  treating 
the  alkaline  filtrate  from  Al,  etc.,  with  H2S  or  ammonium  sulphide 
solution,  and  allowing  to  stand,  covered,  for  a  considerable  time.  A 
more  convenient  method,  which  at  once  separates  the  manganese 
from  accompanying  metals,  is  to  make  the  filtrate  just  acid  with 
sulphuric  acid.  It  is  then  warmed  to  about  70°  C.  and  precip- 
itated by  a  brisk  current  of  H2S  gas.  This  throws  down  zinc, 

i  Handy,  "  Journ.  Am.  Chem.  Soc.,"  XXII,  31. 


ANALYSIS   OF   ORES  AND  SIMILAR  MATERIAL  417 

nickel,  cobalt,  and  also  copper  and  any  other  of  the  heavy  metals 
which  may  be  present,  together  with  any  traces  of  platinum 
which  have  passed  through  from  previous  operations.  The 
precipitate  is  filtered  off  and  washed  with  dilute  H2SO4  containing 
H2S.  The  manganese  is  contained  in  the  filtrate. 

2.  The  ore  is  decomposed  by  treatment  with  hydrochloric 
and  nitric  acids  in  the  usual  way.  It  is  then  heated  to  white 
fumes  with  sulphuric  acid,  cooled  somewhat,  and  diluted  with 
water,  warmed  till  iron  has  dissolved,  and  then  mixed  with  an 
emulsion  of  zinc  oxide  or  pure  precipitated  zinc  hydrate.  This 
precipitates  iron,  leaving  manganese  in  solution.  Filter,  add  a 
saturated  solution  of  bromine  in  water,  and  2  to  3  grams  of  sodium 
acetate.1  On  boiling,  the  manganese  is  precipitated  as  hydrated 
manganese  dioxide.  Boil  and  wash  with  hot  water. 

Estimation.  —  1.  When  manganese  has  been  separated  in 
H2SO4  solution,  as  in  the:  first  method,  the  filtrate  is  made  alka- 
line with  ammonia,  which,  with  the  excess  of  H2S,  causes  the 
manganese  to  precipitate  as  sulphide.  The  flask  is  stoppered 
and  set  aside  over  night,  or  preferably  for  24  hours.  The  clear 
liquid  is  then  decanted  through  a  filter,  the  precipitate  washed 
with  dilute  ammonium  sulphide,  then  dissolved  in  HC1  and 
H2SO4,  boiled  to  expel  excess  of  HC1,  and  the  manganese  deter- 
mined by  any  suitable  gravimetric  or  volumetric  method.  Per- 
haps the  simplest  in  ordinary  circumstances  is  to  add  carbonate 
of  soda  in  slight  excess  to  the  manganese  solution,  which  is  pre- 
viously boiled  in  a  porcelain  or  platinum  vessel.  The  manga- 
nese, precipitated  as  carbonate,  is  filtered  off,  washed  with  hot 
water  till  free  from  alkali,  dried,  ignited  cautiously  in  an  open 
crucible,  and  weighed  as  Mn3O4. 

2.  Where  manganese  has  been  precipitated  by  bromine  as 
MnO2,  it  may  be  conveniently  estimated  by  adding  an  excess  of 
oxalic  acid,  together  with  some  dilute  sulphuric  acid,  heating 
nearly  to  boiling,  diluting  with  water,  and  titrating  the  warm 
solution  with  standard  permanganate,  to  determine  the  excess 
of  oxalic  acid. 

126  parts  crystallized  oxalic  acid  =  55  parts  Mn  or  87  parts  MnO2. 

Reduction  by  oxalic  acid  in  presence  of  dilute  sulphuric  acid 
affords  an  easy  means  of  determining  the  amount  of  actual  MnO2 

1  For  details  see  A.  H.  Low,  "Technical  Methods  of  Ore  Analysis,"  3d  edition, 
p.  146. 


418  THE  CYANIDE   HANDBOOK 

in  a  manganese  ore  when  other  oxides  are  present,  as  the  latter 
do  not  oxidize  oxalic  acid  under  the  conditions  of  the  test. 

3.  Very  small  quantities  of  manganese  are  best  determined 
by  the  colorimetric  method;  l  the  ore  is  oxidized  by  boiling  with 
nitric  acid  and  lead  peroxide,  and  the  tint  of  the  resulting  solu- 
tion compared  with  that  of  a  standard  permanganate  solution 
containing  a  known  quantity  of  manganese. 

For  further  details  on  the  estimation  of  manganese  see  Berin- 
ger,  "Text  Book  of  Assaying,"  pp.  299-306,  and  Sutton,  "Volu- 
metric Analysis,  8th  edition,  pp.  255-266." 

MERCURY 

Gold  and  silver  ores  occasionally  contain  cinnabar,  and  metal- 
lic mercury  is  frequently  present  in  such  products  as  tailings  and 
concentrates,  so  that  its  determination  may  be  of  importance  in 
connection  with  the  cyanide  process.  Whenever  possible,  sev- 
eral pounds  of  the  sample  should  be  carefully  panned,  in  cases 
where  the  presence  of  metallic  mercury  is  suspected.  If  floured, 
the  metal  may  generally  be  obtained  in  a  single  globule  by  the 
addition  of  cyanide  or  ammonium  chloride. 

Estimation.  —  1.  The  following  rough  method  frequently 
suffices.  The  powdered  sample,  mixed  with  soda-lime,  is  placed 
in  a  porcelain  crucible  covered  with  a  disk  of  gold  or  silver  shaped 
like  a  watch-glass,  the  hollow  side  uppermost  and  filled  with 
water.  The  mixture  is  cautiously  heated;  the  cinnabar  or  other 
ore  is  decomposed,  and  the  volatilized  mercury  condenses  on 
the  under  side  of  the  disk.  When  the  action  is  complete,  the 
disk  is  removed,  washed  with'  alcohol,  and  dried  in  a  desiccator. 
It  is  then  weighed,  the  increase  of  weight  giving  the  amount  of 
mercury  deposited. 

2.  The  mineral  may  also  be  mixed  with  lime  and  heated  in  a 
combustion  tube  closed  at  one  end.  The  closed  end  is  previously 
filled  with  powdered  magnesium  carbonate.  The  open  end  is 
bent  and  drawn  to  a  point,  dipping  under  water.  The  carbonic 
acid  evolved  from  the  magnesium  carbonate  drives  out  the  last 
portions  of  mercury  vapor;  the  sublimed  mercury  is  condensed 
by  the  water,  collected,  dried,  and  weighed.2 

1  Beringer,  loc.  tit.,  p.  306. 

2  Beringer,  loc.  tit.,  p.  172. 


ANALYSIS   OF   ORES   AND  SIMILAR  MATERIAL  419 

NICKEL 

Separation.  —  Proceed  as  described  under  cobalt,  until  a 
solution  is  obtained  containing  only  these  metals.  In  cases 
where  a  separation  of  the  two  metals  is  necessary,  precipitate  the 
cobalt  as  described,  with  potassium  nitrite,  filter,  precipitate 
the  nickel  from  a  boiling  solution,  by  caustic  alkali,  filter,  and 
wash  with  hot  water. 

Estimation.1  —  Dissolve  the  precipitate  of  nickel  hydroxide 
in  dilute  ammonia.  Add  a  measured  quantity  of  a  solution  of 
potassium  cyanide  which  has  been  accurately  standardized  on  a 
silver  nitrate  solution  of  known  strength,  using  potassium  iodide 
indicator.  If  the  nickel  precipitate  does  not  dissolve  readily  in 
ammonia,  add  a  little  ammonium  chloride.  When  sufficient 
cyanide  has  been  added  to  give  a  perfectly  clear  solution,  a  mod- 
erate excess  is  added  beyond  this  point,  then  potassium  iodide 
is  added,  and  the  excess  of  cyanide  titrated  by  means  of  the 
standard  silver  solution.  Cobalt  and  nickel  may  be  estimated 
together  by  this  method,  but  the  presence  of  cobalt  causes  a 
darkening  of  the  solution.  The  cyanide  solution  should  also  be 
standardized  on  a  nickel  solution  of  known  strength. 

OXYGEN 

In  most  cases  the  amount  of  oxygen  in  an  ore  can  only  be 
determined  by  difference,  after  all  other  ingredients  have  been 
estimated.  Sulphates  and  carbonates  are  separately  deter- 
mined and  their  oxygen  contents  calculated.  The  nature  and 
degree  of  oxidation  of  the  metallic  oxides  present  may  sometimes 
be  ascertained  by  examining  uncrushed  specimens  of  the  ore. 
In  a  few  cases  oxygen  may  be  directly  determined  (e.g.,  in  cas- 
siterite)  by  igniting  the  ore  in  a  stream  of  hydrogen  and  collect- 
ing the  water  formed  by  means  of  a  suitable  absorbent  in  a 
weighed  tube.  The  hydrogen  must  of  course  be  previously  dried 
and  freed  from  any  admixed  oxygen,  and  any  combined  water 
present  in  the  mineral  must  be  previously  expelled,  or  allowed 
for  in  the  determination.  In  cases  where  oxides  of  a  given  metal 
in  various  degrees  of  oxidation  are  present  in  an  ore,  methods 
may  be  employed  for  determining  one  or  other  of  these  separately 
and  deducing  the  amount  of  the  other  from  the  total  quantity 

'  T.  Moore,  "Chem.  News,"  LXXII,  92. 


420  THE  CYANIDE   HANDBOOK 

of  the  given  metal.  Thus  in  an  ore  containing  ferrous  and  ferric 
oxides,  we  may  determine  the  total  iron,  and  the  iron  present  as 
ferrous  oxide,  by  separate  tests.  A  simple  calculation  then  gives 
the  amount  of  each  oxide  present. 

PHOSPHORIC    ACID 

Separation.  —  Ores  frequently  contain  small  quantities  of 
phosphoric  acid  in  the  form  of  metallic  phosphates,  and  calcium 
phosphate  is  found  pure  or  mixed  with  other  minerals.  Most 
phosphates  are  soluble  in  hydrochloric  acid. 

1.  Boil   with   hydrochloric   acid,    filter,   ignite   the   insoluble 
residue  in  a  platinum  crucible  and  add  it  to  the  extract.     Evap- 
orate the  whole  to  dryness.     Take  up  the  residue  with  nitric 
acid,  concentrate  by  boiling,  dilute,  filter,  and  wash  with  water. 
Precipitate  the  warm  filtrate  with  a  warm  clear  solution  of  am- 
monium  nitro-molybdate,  which  gives  a  yellow  precipitate  on 
standing. 

2.  In  cases  where  arsenic  is  present,  take  up  the  evaporated 
residue  with  HC1  instead  of  HNO3,  precipitate  the  As  with  H2S, 
filter,  boil  off  excess  of  H2S,  then  add  HNO3  and  proceed  as  above, 
adding  ammonium  nitro-molybdate. 

3.  The  substance  is  treated  with  HC1  as  already  described, 
evaporated  to  dryness,  taken  up  with  HC1,  diluted  and  precip- 
itated with  H2S.     The  precipitate  is  filtered  off  and  the  filtrate 
boiled  to  expel  excess  of  H2S  and  treated  with  HNO3.     Ferric 
chloride  is  then  added,  if  sufficient  iron  is  not  already  present, 
to  convert  the  whole  of  the  phosphoric  acid  into  ferric  phosphate ; 
the  solution  is  then  just  neutralized  with  ammonia,  sodium  ace- 
tate and  acetic  acid  added,  boiled  slightly,  and  filtered.     The 
precipitate,  after  washing,  is  transferred  to  a  flask  and  treated 
with  ammonia  and  H2S  to  remove  the  iron.     It  is  then  filtered,  the 
filtrate  containing  the  phosphoric  acid  as  ammonium  phosphate. 

Estimation.  —  1.  When  the  phosphate  has  been  separated 
with  nitro-molybdate,  the  precipitate  is  collected  on  a  weighed 
filter-paper,  and  washed,  first  with  dilute  nitric  acid,  then  with 
alcohol,  dried  at  110°  and  weighed  as  ammonium  phospho- 
molybdate  (NH4)3  •  12MoO3  •  P<V 

Weight  of  precipitate  X  0.0165  =  P. 
1  "  Journ.  Am.  Chem.  Soc.,"  XIX,  614. 


ANALYSIS   OF   ORES   AND  SIMILAR  MATERIAL  421 

2.  The  molybdate  precipitate  is  collected  on  an  unweighed 
filter,  washed  with  acid  ammonium  sulphate,  then  dissolved  in 
ammonia.     The  solution  is  reduced  with  powdered  zinc  and  sul- 
phuric acid,  and  titrated  at  40°  C.  with  permanganate,  which 
oxidizes  Mo2O3  to  2MoO3. 

3.  The  molybdate  precipitate  is  washed  with   10  per  cent, 
ammonic  nitrate,  dissolved  in  dilute  ammonia,  and  precipitated 
with  "magnesia  mixture"  (MgSO4,  NH4C1,  and  NH4OH).     The 
precipitate,  after  standing  for  some  time,  is  filtered  and  washed 
with  dilute  ammonia  and  dissolved  in  HC1,  made  just  alkaline 
with  ammonia,  mixed  with  acetic  acid  and  sodium  acetate  till 
distinctly  acid,    and   titrated  with    standard   uranium    acetate, 
with  ferrocyanide  indicator  exactly  as  in  the  case  of  arsenic. 
(See  above.) 

4.  The  phosphate  solution,  after  precipitation  as  ferric  phos- 
phate and  removal  of  iron  as  described  in  separation  method 
No.  3,  is  acidulated  with  HC1  and  titrated  with  uranium  acetate 
as  above. 

POTASSIUM 

The  methods  of  separating  the  alkali  metals  from  other  ele- 
ments have  already  been  described.  (See  above.) 

Estimation.  —  1.  In  cases  where  considerable  amounts  of 
both  sodium  and  potassium  are  present,  the  quantity  of  potas- 
sium may  be  deduced  by  calculation,  after  weighing  the  mixed 
chlorides  and  titrating  the  chlorine,  by  means  of  the  formula: 

K  =  2.44  M  —  4.024  Cl,  when 
K  =  weight  of  potassium  in  portion  analyzed, 
M  =  weight  of  mixed  chlorides  found, 
Cl  =  weight  of  chlorine  found. 

The  sodium  is  of  course  found  by  difference. 

2.  In  cases  where  an  exact  estimation  of  potassium  is  neces- 
sary, the  final  residue  after  ignition  is  not  titrated  for  chlorine, 
but  dissolved  in  water  and  mixed  with  a  solution  of  platinic 
chloride  (H2PtCl6)  containing  3  parts  of  platinum  for  every  part 
of  the  mixed  sodium  and  potassium  chlorides  present.1  It  is 
then  evaporated  on  a  water-bath  nearly  to  dryness,  moistened 
again  with  the  platinum  solution,  covered  with  alcohol,  and 
washed  by  rotating  the  dish.  After  settling,  the  liquid  is  de- 

1  Tatlock's  method.     See  also  A.  II.  Low,  "Technical  Methods  of  Ore  Analy- 
sis," 3d  edition,  p.  184. 


422  THE  CYANIDE  HANDBOOK 

canted  through  a  filter  and  the  precipitate  washed  with  alcohol 
until  the  filtrate  is  perfectly  colorless.  The  residue  in  the  dish 
is  then  washed  on  to  the  filter,  using  as  little  alcohol  as  possible, 
finally  washing  once  or  twice  on  the  filter  by  means  of  a  small 
wash-bottle  containing  alcohol  and  provided  with  a  fine  jet. 
The  precipitate  is  then  dried  on  the  paper  in  the  water-oven  and 
transferred  to  a  weighed  crucible.  It  may  be  weighed  directly 
as  potassium  platino-chloride  (K2PtCl6).  The  paper  is  ignited 
and  weighed  as  Pt  +  2KC1  +  ash. 

K2PtCl6  X  0.30561  =  KCL 

K2PtCl6  X  0.1612  =  K. 
(Pt  +  2KC1)  X  0.2276  =  K. 

3.  In  cases  where  the  sodium  largely  exceeds  the  potassium, 
Finkener's  method,  as  modified  by  Dittmar  and  Mac  Arthur,  is 
preferable.1  Having  obtained  the  residue  of  mixed  chlorides  as 
before,  add  platinic  chloride  (H2PtCl6)  containing  at  least  3.2 
parts  of  platinum  for  every  part  of  potassium  present.  Add  a 
little  water  and  heat  till  the  precipitate  just  dissolves,  evaporate 
on  a  water-bath  to  a  small  bulk  and  stir  to  prevent  formation  of 
large  crystals.  Cool,  add  10  cc.  absolute  alcohol,  then  after 
some  time  5  cc.  of  ether;  stir,  allow  to  stand,  covered,  for  some 
hours  till  the  precipitate  is  thoroughly  settled.  Decant  through 
a  filter,  and  wash  with  a  mixture  of  1  vol.  ether  and  2  vols.  alco- 
hol. In  some  cases  it  may  be  necessary  to  re-dissolve  the  pre- 
cipitate in  water  and  re-crystallize  by  evaporation  and  addition 
of  alcohol,  as  before.  When  washed  free  from  platinum  salts 
(Na2PtCl6)  transfer  the  precipitate  to  a  conical  flask,  add  1  cc. 
water  for  every  5  mg.  of  platinum  estimated  to  be  present  in 
the  precipitate.  Immerse  the  flask  containing  the  precipitate 
in  a  water-bath  at  90°  C.  and  pass  in  a  current  of  purified  hydro- 
gen until  the  solution  becomes  perfectly  colorless  and  the  whole 
of  the  platinum  is  precipitated;  thus: 

K2PtCl6  +  4H  =  4HC1  +  2KC1  +  Pt. 

Filter,  wash  with  hot  water,  ignite  and  weigh  the  platinum. 

Pt  X  0.402  =  K. 

SELENIUM 

Selenium  and  tellurium  are  not  infrequently  associated  with 
gold  or  silver  in  ores,  and  are  obtained,  together  with  sulphur, 

1 W.  Dittmar,  "Exercises  in  Quantitative  Analysis,"  pp.  25-30,  310-313. 


ANALYSIS   OF   ORES   AND  SIMILAR  MATERIAL  423 

by  the  methods  given  under  that  heading,  as  selenates  and  tel- 
lurates.  These  compounds  are  less  perfectly  precipitated  than 
sulphates  by  addition  of  barium  chloride. 

Detection.  —  The  ore  is  extracted  with  nitro-hydrochloric 
acid,  or  fused  with  sodium  carbonate  and  niter  and  extracted 
with  HC1.  The  nitrate  is  evaporated  on  a  water-bath  several 
times  with  HC1,  adding  a  little  NaCl  in  the  first  case,  until  all 
nitrates  are  expelled.  On  adding  sodium  sulphite  to  the  solu- 
tion and  heating  to  boiling,  selenium  gives  a  red  precipitate, 
becoming  black  on  continued  boiling.  Tellurium  gives  at  once 
a  black  precipitate. 

Separation.  —  Having  obtained  a  hydrochloric  acid  extract 
free  from  nitric  acid,  pass  a  current  of  purified  SO2  gas  into  the 
boiling  liquid,  until  the  precipitate  comes  down  in  a  dense  form. 
It  is  then  collected  on  a  weighed  filter-paper,  washed  rapidly 
with  dilute  SO2  water,  dried  at  100°  C.,  and  weighed  as  xSe  + 
yTe.  To  separate  selenium  and  tellurium  the  dry  precipitate 
is  mixed  with  about  10  times  its  weight  of  powdered  potassium 
cyanide  and  fused  in  an  atmosphere  of  hydrogen.  The  melt  is 
extracted  with  water,  filtered  if  necessary,  and  a  current  of  air 
passed  through  the  filtrate  for  some  time.  Tellurium  alone  is 
precipitated,  being  present  as  potassium  telluride,  which  grad- 
ually decomposes  under  the  influence  of  air.  Selenium  remains 
in  solution  as  KSeCN.  After  collecting  the  tellurium  on  a 
weighed  filter,  the  liquid  is  acidulated  with  HC1  and  Se  precip- 
itated. 

Estimation.  —  Selenium  is  determined  by  collecting  the  pre- 
cipitate obtained  as  above  on  a  weighed  filter  paper,  drying  at 
100°  C.  and  weighing  as  Se.  Small  quantities  may  be  estimated 
with  sufficient  accuracy  by  comparing  the  tint  of  the  emulsion 
with  that  obtained  by  boiling  measured  quantities  of  a  sodium 
selenite  solution  of  known  strength  with  HC1  and  a  sulphite. 

SILICA 

A  portion  (in  ordinary  cases  1  gram)  of  the  crushed  sample, 
previously  dried  at  100°  or  110°  C.,  is  weighed  in  a  weighing  bottle 
and  transferred  to  a  tolerably  capacious  platinum  crucible.  This 
is  placed  in  an  inclined  position  and  heated,  cautiously  at  first, 
by  allowing  the  oxidizing  flame  of  a  Bunsen  burner  or  similar 
appliance  to  play  on  the  outside  of  the  crucible  at  the  bottom 


424  THE  CYANIDE  HANDBOOK 

and  round  the  sides.  The  crucible  is  moved  from  time  to  time 
to  allow  the  contents  to  be  uniformly  heated  and  to  prevent 
caking.  The  object  of  this  operation  is  to  remove  all  oxidizable 
and  volatile  material  such  as  sulphur,  arsenic,  etc.,  which  might 
injure  the  crucible  in  the  subsequent  fusion. 

After  the  ignition  is  complete,  the  crucible  is  allowed  to  cool 
and  its  contents  intimately  mixed  with  6  or  7  grams  of  the 
purest  obtainable  anhydrous  sodium  carbonate,  finely  powdered. 
The  crucible  is  then  gradually  raised  to  a  bright-red  heat,  main- 
taining an  oxidizing  atmosphere  until  the  contents  are  thoroughly 
fused  and  there  are  no  signs  of  effervescence.  It  is  then  allowed 
to  cool,  cleaned  externally  if  necessary,  and  immersed  in  an 
evaporating  dish,  preferably  of  platinum,  containing  warm 
water,  to  which  sufficient  hydrochloric  acid  is  added  to  render 
the  liquid  slightly  acid.  The  mass  generally  disintegrates,  and 
can  then  be  detached  from  the  crucible;  the  latter  is  carefully 
washed  and  removed,  and  the  liquid  evaporated,  finally,  over  a 
water-bath  until  nearly  dry.  The  mass  is  then  re-dissolved  in 
dilute  HC1,  warmed  and  filtered.  The  filtrate,  which  may  contain 
about  1  per  cent,  of  silica,  is  again  evaporated  on  the  water- 
bath,  taken  up  with  dilute  acid  and  filtered,  best  on  a  sepa- 
rate filter.  The  precipitates  are  thoroughly  washed  with  hot 
water  and  the  additional  silica  added  to  the  main  portion.  The 
united  filtrate  is  reserved  for  estimation  of  alumina,  iron,  etc. 
It  may  still  contain  0.1  per  cent,  of  silica,  which  is  separated 
later. 

The  precipitate  is  dried  with  the  filter-papers  in  an  air-bath, 
then  transferred  to  a  platinum  crucible,  ignited  strongly,  allowed 
to  cool  in  a  desiccator  and  weighed  in  the  covered  crucible,  as 
the  finely-divided  silica  is  very  hygroscopic.  The  substance 
thus  obtained  nearly  always  contains  some  impurity,  and  in 
accurate  work  should  be  examined  by  treating  the  whole,  or  an 
aliquot  part,  with  a  mixture  of  sulphuric  and  hydrofluoric  acids, 
heating  the  platinum  crucible  until  the  whole  of  the  silica  is 
expelled.  The  crucible  and  residual  contents  are  then  weighed; 
this  weight,  deducted  from  the  previous  one,  gives  the  amount 
of  silica  in  the  portion  of  substance  examined. 

The  method  here  described  is  inapplicable  in  presence  of  lead 
or  other  heavy  metals  liable  to  attack  platinum,  or  in  presence 
of  fluorides.  In  these  cases  the  interfering  substances  must  be 


ANALYSIS   OF  ORES   AND  SIMILAR  MATERIAL  425 

removed   by   preliminary   operations   before   the   estimation   of 
silica  is  made. 

SODIUM 
See  ALKALI  METALS  and  POTASSIUM. 

STRONTIUM 
See  BARIUM. 

SULPHUR 

Sulphur  exists  in  ores  usually  in  the  form  of  metallic  sulphides, 
and  to  a  less  extent  as  sulphates.  Its  estimation,  particularly 
in  concentrates  and  similar  products,  may  sometimes  be  impor- 
tant, and  in  some  cases  useful  information  may  be  obtained  by 
determining  the  mode  of  combination  in  which  the  sulphur 
occurs. 

Separation.  —  1.  In  certain  cases  sulphur  may  be  brought 
into  solution  by  evaporating  with  nitric  acid  or  aqua  regia,  which 
convert  it  into  sulphuric  acid  or  a  metallic  sulphate.  In  this 
connection  it  is  well  to  remember  that  when  iron  pyrites  is  oxi- 
dized with  nitric  acid  a  portion  of  the  sulphur  is  necessarily  con- 
verted into  free  sulphuric  acid: 

2FeS2  +  15O  +  H2O  =  Fe2(SO4)3 


and  may  be  lost  if  the  evaporation  is  carried  too  far,  unless  some 
base,  e.g.,  Na2CO3,  be  added. 

2.  A  more  -general  method  is  to  fuse  the  finely  powdered 
mineral  in  a  covered  platinum  dish  or  crucible  with  an  excess  of 
niter,  to  which  sodium  carbonate  is  added  if  the  amount  of  sul- 
phides is  large.  The  fusion  is  conducted  at  a  low-red  heat,  and 
the.  mass  is  extracted  with  water  and  filtered,  most  of  the  other 
constituents  remaining  insoluble. 

Estimation.  —  1.  The  extract  in  either  case  is  freed  as  much 
as  possible  from  nitric  acid  by  evaporation  with  HC1,  then  diluted 
considerably,  heated  to  boiling,  and  precipitated  with  barium 
chloride.  After  standing  for  some  time,  the  clear  liquid  is  poured 
off  through  a  filter,  the  residue  washed  several  times  by  decanta- 
tion  with  boiling  water  containing  a  few  drops  of  HC1,  filtered, 
washed,  dried,  ignited  at  a  moderate  red  heat,  and  weighed  as 
BaSO4. 

BaSO4  X  0.1373  =  S. 


426  THE  CYANIDE  HANDBOOK 

2.  Sulphur  may  also  be  estimated  volumetrically.     For  this 
purpose  the  HC1  extract  is  concentrated  to  a  small  bulk,  mixed 
with  sodium  acetate  and  acetic  acid,  diluted  considerably,  and 
boiled.     Standard  barium  •  chloride  solution  is  then  run  into  the 
boiling  liquid,  contained  in  a  large  dish,  until  a  portion  of  the 
liquid,  taken  out  and  filtered,  begins  to  give  a  slight  turbidity 
with  dilute  sulphuric  acid. 

3.  In  ores  containing  sulphate  of  lead,  the  latter  is  extracted 
by  treating  with  hot  concentrated  ammonium  acetate,  and  the 
sulphate   collected    and  determined    as  described    under    LEAD. 
Ores  containing  CaSO4,  BaSO4,  or  SrSO4  are  fused  with  sodium 
carbonate  and  the  sulphur  determined  in  the  aqueous  extract. 
(See  BARIUM.) 

TELLURIUM 

For  methods  of  separation  and  estimation,  see  SELENIUM. 

Detection.  —  The  presence  of  small  traces  of  tellurium  may 
be  detected  by  boiling  the  substance  with  nitric  acid,  then  evap- 
orating with  strong  sulphuric  acid  until  white  fumes  appear:  on 
cooling  somewhat,  a  strip  of  tin-foil  is  added  to  the  liquid,  when 
a  fine  purple  color  appears  if  tellurium  be  present. 

Tellurium  or  selenium  may  sometimes  be  present  in  the  pre- 
cipitate of  BaSO4,  obtained  in  the  estimation  of  sulphur  as  ba- 
rium tellurate  (BaTe04)  or  barium  selenate  (BaSeOJ.  In  this 
case  the  precipitate  should  be  fused  with  sodium  carbonate,  and 
the  aqueous  extract  acidified  with  HC1  and  treated  with  SO2,  as 
described  under  SELENIUM. 

TIN 

Ores  such  as  are  treated  by  the  cyanide  process  rarely  con- 
tain much  tin.  When  present  in  minute  quantities,  the  metal 
is  detected  and  estimated  with  great  difficulty.  The  method  of 
separating  tin  from  arsenic  and  antimony  is  given  under  ANTI-T 
MONY. 

Estimation.  —  1 .  Where  the  amount  is  sufficient,  the  following 
method  1  may  be  used.  The  ore  is  crushed  coarsely  and  concen- 
trated by  vanning.  About  20  grams  of  the  concentrates  are  then 
extracted  with  aqua  regia  to  remove  the  bulk  of  the  other  metals 
which  may  be  present,  SnO2  being  practically  insoluble  in  this 
reagent.  After  washing  and  filtering,  the  residue  on  the  filter- 

'C.  and  J.  Beringer,     "Text  Book  of  Assaying,"  9th  edition,  p.  278. 


ANALYSIS   OF   ORES  AND  SIMILAR  MATERIAL          427 

paper  is  placed  in  a  fire-clay  crucible,  size  E,  and  calcined,  then 
mixed  with  its  own  weight  of  potassium  cyanide.  An  equal 
weight  of  cyanide  is  added  as  a  cover,  and  the  whole  is  fused. 
The  pot  is  then  removed  from  the  furnace,  tapped,  and  the  con- 
tents poured  into  a  mold.  The  slag  is  dissolved  in  water,  and 
the  button  of  metallic  tin  cleaned  and  weighed. 

2..  Tin  may  also  be  estimated  by  fusing  the  oxidized  and 
roasted  mineral  with  soda  under  a  cover  of  charcoal,  in  an  iron, 
nickel,  or  silver  crucible.  The  molten  mass  is  dissolved  in  strong 
hydrochloric  acid,  and  the  tin,  after  reducing  to  stannous 
chloride,  titrated  by  means  of  a  solution  of  iodine  in  potassium 
iodide.  This  method  may  be  used  in  presence  of  arsenic  and 
antimony,  provided  the  solution  is  sufficiently  acid. 

TITANIUM 

.  This  metal,  which  is  frequently  present  in  small  quantities 
in  siliceous  ores,  may  be  conveniently  estimated  in  the  solution 
obtained  during  the  separation  of  barium,  by  treating  the  res- 
idue after  evaporation  with  H2SO4  and  HF  with  5  per  cent, 
sulphuric  acid.  The  titanium  in  this  solution  is  estimated  colori- 
metrically  by  comparing  the  tint  produced  by  the  addition  of 
about  2  cc.  of  hydrogen  peroxide,  free  from  fluorine,  with  that 
produced  under  similar  conditions  with  measured  quantities  of 
normal  solution  of  titanium  sulphate.  A  dark-brown  color 
appears  on  addition  of  the  hydrogen  peroxide. 

WATER 

The  determination  of  moisture  or  "hygroscopic  water"  has 
already  been  described,  under  PRELIMINARY  OPERATIONS.  In 
addition  to  this,  many  ores  contain  combined  water.  In  most 
cases  it  is  sufficient  to  determine  the  total  quantity  of  water 
not  driven  off  at  100°  or  110°  C.  The  ore  is  first  carefully  dried 
at  this  temperature  until  the  weight  of  the  sample  in  consecutive 
weighings  at  intervals  of  (say)  half  an  hour  remains  constant. 
The  sample  is  then  heated  in  a  hard  glass  tube  connected  with 
weighed  tubes  containing  sulphuric  acid  or  other  absorbents, 
and  arranged  so  that  a  current  of  dry  air  can  be  aspirated  suc- 
cessively through  the  heated  tube  and  the  absorption  apparatus. 
In  cases  where  other  volatile  substances  are  given  off  which 


428  THE  CYANIDE  HANDBOOK 

would  interfere  with  the  determination,  the  ore  may  be  mixed 
with  a  dry  alkali,  such  as  calcined  magnesia  or  anhydrous  sodium 
carbonate.  In  some  cases  it  is  necessary  to  collect  the  water 
in  a  cooled  condenser  instead  of  absorbing  in  the  manner 
described.  In  a  few  cases  a  white  heat  is  necessary  for  complete 
expulsion  of  combined  water. 

ZINC 

Ores  of  zinc,  such  as  blende  and  calamine,  occur  pretty  fre- 
quently associated  with  gold-  and  silver-bearing  minerals.  Zinc 
is  also  an  invariable  constituent  of  slags  produced  in  the  smelting 
of  zinc-gold  precipitate  in  the  cyanide  process. 

Separation.  —  Zinc  is  usually  determined  in  the  nitrate 
after  separation  of  iron  and  alumina.  In  cases  where  manganese 
also  is  present,  the  latter  may  be  removed  by  boiling  with  bro- 
mine water  in  presence  of  an  excess  of  ammonia,  or  the  zinc 
may  be  precipitated  as  sulphide  from  a  warm  solution  rendered 
faintly  acid  with  sulphuric  or  acetic  acid,  manganese  remaining 
in  solution.  An  excess  of  ammonium  chloride  should  be  present 
in  either  case.  When  the  zinc  has  been  obtained  as  sulphide, 
free  from  other  metals,  filter,  wash  with  boiling  water  containing 
a  little  ammonium  sulphide;  finally  dissolve  the  precipitate  in 
HC1,  boil  to  expel  H2S,  and  filter.  Where  copper  and  other 
heavy  metals  are  present,  they  are  first  precipitated  by  H2S  from 
a  strongly  acid  (HC1)  solution,  before  separating  the  zinc. 

Estimation.  —  1.  Where  the  quantity  is  considerable,  make 
slightly  acid  with  HC1,  dilute  to  about  250  cc.,  heat  to  boiling, 
cool  to  70°  C.,  and  add  a  standard  solution  of  potassium  ferro- 
cyanide  (about  2  per  cent.  K4FeCy6  •  3H2O)  until  a  drop  taken 
out  shows  a  brown  coloration  with  a  spot  of  uranium  acetate  or 
nitrate  on  a  porcelain  plate.  Add  about  5  cc.  ferrocyanide  in 
excess.  Warm  gently  for  ten  minutes,  and  titrate  the  excess 
with  a  standard  zinc  chloride  solution  of  corresponding  strength, 
until  a  color  is  no  longer  produced. 

2.  Where  the  amount  of  zinc  is  small,   precipitate   as  sul- 
phide, filter,  dry  with  the  filter-paper  at  the  mouth  of  a  muffle, 
ignite,  first  at  a  low  temperature,  finally  at  a  red  heat,  and  weigh 
as  ZnO. 

3.  The  following  method  is  given  by  H.  T.  Waller  l  for  deter- 

i  "Bull.  I.  M.  M.,"  No.  49,  Oct.  8,  1908. 


ANALYSIS   OF  ORES   AND  SIMILAR  MATERIAL  429 

mining  zinc  in  slags.  The  sample  for  analysis,  0.5  gram,  is 
moistened  with  water,  5  cc.  HC1  added,  and  rubbed  till  gelatinous 
silica  separates.  It  is  then  evaporated  to  dryness  at  a  moderate 
heat,  finally  on  a  hot  plate,  to  render  silica  insoluble.  Take  up 
residue  with  20  cc.  of  a  saturated  solution  of  KC1O3  in  HNO3. 
Evaporate  in  a  covered  dish  to  complete  dryness.  By  this 
treatment  MnO2  remains  insoluble.  Add  7  grams  solid  NH4C1, 
20  cc.  ammonia,  and  25  cc.  hot  water.  Stir,  boil,  and  filter.  If 
much  iron  is  present,  re-dissolve  in  KC1O3  and  HNO3  and  again 
evaporate  to  dryness.  In  presence  of  copper  add  granulated 
or  sheet  lead  and  boil.  Dilute  filtrate  to  75  cc.,  heat  to  70°  C. 
and  titrate  with  ferrocyanide  as  above. 


SECTION  II 

ANALYSIS  OF  BULLION  AND  OTHER  MAINLY  METAL- 
LIC  PRODUCTS 

IN  this  section  we  shall  discuss  only  the  analysis  of  matter 
composed  entirely  or  mainly  of  metallic  elements,  such  as  gold 
and  silver  bullion,  mattes,  skimmings,  and  other  by-products. 
Useful  information  may  sometimes  be  obtained  by  an  analysis 
of  the  zinc-box  precipitate,  roasted  or  unroasted,  in  order  to 
determine  the  best  method  of  fluxing  the  same.  Occasionally 
an  analysis  may  be  required  of  such  products  as  the  "  white  pre- 
cipitate" in  the  zinc-boxes. 

We  may  classify  the  ingredients  to  be  determined  as  follows: 
(1)  Gold  and  silver.  (2)  Base  metals,  more  particularly  zinc, 
copper,  and  lead;  in  smaller  quantities,  iron,  arsenic,  antimony, 
and  occasionally  manganese,  nickel,  and  cobalt.  (3)  Non-metals, 
chiefly  sulphur,  also  small  amounts  of  carbon,  silicon,  phosphorus, 
selenium,  and  tellurium. 

SAMPLING  AND  PRELIMINARY  OPERATIONS 

Low-grade  bullion  is  best  sampled  by  "  dipping "  while  in 
the  molten  condition,  just  before  pouring.  (See  Part  VII.)  With 
high-grade  bullion,  drill  samples  are  admissible  and  in  some  cases 
preferable.  Matte  may  generally  be  sampled  by  crushing  and 
quartering  in  the  manner  described  for  ores.  Gold-cyanide  pre- 
cipitates and  similar  material  require  extremely  careful  sampling. 
Accurate  results  can  only  be  obtained  by  passing  a  large  part 
of  the  dried  precipitate  through  a  fine  sieve,  and  making  separate 
determinations  on  the  portions  remaining  on  and  passing  the 
sieve.  In  some  cases  the  samples  contain  comparatively  large 
pieces  of  metal,  which  may  be  hammered  out  or  passed  between 
rolls,  and  finally  cut  in  small  pieces  with  clean  scissors.  In  every 
case  the  particles  should  be  reduced  to  as  fine  a  state  of  sub- 
division as  possible,  and  thoroughly  mixed  before  selecting  the 

430 


ANALYSIS   OF   BULLION  AND   METALLIC   PRODUCTS    431 

necessarily  small  portion  taken  for  the  actual  analysis.  Any 
particles  of  slag  or  other  matter  obviously  not  forming  a  legiti- 
mate part  of  the  sample  should  be  carefully  picked  out.  The 
weight  taken  for  analysis  is  usually  0.5  gram  to  1  gram.  Owing 
to  the  very  varied  nature  of  the  materials  dealt  with  it  is  im- 
possible to  give  a  universally  applicable  scheme  of  analysis, 
and  •  only  the  more  important  determinations  will  be  here 
described.  Reference  should  also  be  made  to  Section  I  (Ore 
Analysis) . 

ESTIMATION  OF  PRECIOUS  METALS 

GOLD 

This  is  usually  made  by  fire  assay  (see  Part  VII),  but  there 
are  cases  where  wet  methods  are  desirable,  as,  for  instance,  with 
certain  materials  heavily  charged  with  copper  and  other  base 
metals.  In  any  case  a  wet  method  of  separating  gold  must  be 
used  if  other  constituents  are  to  be  determined.  The  procedure 
will  depend  largely  on  the  amount  of  gold  present. 

1.  Where  the  gold  constitutes  more  than  (say)  30  per  cent, 
of  the  material,  it  may  in  most  cases  be  dissolved  in  aqua  regia. 
With  alloys  containing  a  certain  proportion  of  silver,  however, 
this  is  very  tedious,  as  the  particles  of  metal  rapidly  become 
coated  with  a  deposit  of  silver  chloride  which  stops  any  further 
action.     This  may  be  overcome  by  alternate  treatments  with 
aqua  regia  and  ammonia,  but  even  in  this  way  the  process  is 
very  slow.     A  mixture  of  HC1  and  KC1O3  is  more  effective  than 
aqua  regia,  as  when  sufficiently  concentrated  it  keeps  AgCl  in 
solution;  the  silver  may  be  precipitated  as  chloride,  after  all  the 
gold  has  dissolved,  by  diluting  considerably,  heating,  and  settling. 

2.  Another  method,  applicable,  however,  only  in  the  absence 
of  volatile  constituents,  is  to  fuse  the  bullion  in  a  covered  porce- 
lain crucible  with  five  or  six  times  its  weight  of  some  very  fusible 
metal,  such  as  cadmium,  under  a  layer  of  cyanide.1     The  resulting 
alloy,  after  cleaning,  is  then  dissolved  in  dilute  and  finally  in 
75  per  cent,  nitric  acid,  the  insoluble  matter  being  chiefly  gold. 

3.  Where  the  alloy  contains  sufficient  silver  or  other  metal 
for  parting  the  gold  in  nitric  acid,  it  may  be  dissolved  at  once  in 
that  acid.     Two  treatments  are  usually  sufficient,  using  acid  of 
75  per  cent,  by  volume.     The  residue  is  washed  several  times  by 

1  Beringei',  "Text  Book  of  Assaying,"  9th  edition,  p.  157. 


432  THE  CYANIDE   HANDBOOK 

decantation  with  hot  water,  dried,  ignited,  and  weighed.  It 
should  then  be  dissolved  in  aqua  regia,  diluted,  and  allowed  to 
stand  and  settle  clear.  The  residue  is  filtered  off  and  its  weight 
determined  after  careful  drying.  Any  silver  present  will  of 
course  have  been  converted  into  chloride,  and  its  amount  may 
be  determined  by  cupeling  the  dry  residue  with  lead.  The 
proper  correction  can  then  easily  be  calculated,  to  obtain  the  true 
weight  of  gold  in  the  sample. 

4.  In  cases  where  the  alloy  is  soluble  in  aqua  regia  the  gold 
may  be  precipitated  by  oxalic  or  sulphurous  acids.  For  this 
purpose  the  liquid  should  be  concentrated  to  a  small  bulk  on  the 
waterrbath  and  re-evaporated  several  times  with  HC1  until 
practically  all  HNO3  is  removed.  The  residue  is  then  diluted, 
heated  to  boiling,  filtered  if  necessary,  and  the  precipitant  added. 
A  current  of  purified  SO2  gas  is  the  best  for  the  purpose,  as  it 
introduces  no  substance  which  can  interfere  with  subsequent 
operations.  A  few  other  elements,  such  as  selenium  and  tellu- 
rium, are,  however,  precipitated  along  with  the  gold  by  this  re- 
agent. After  settling,  the  liquid  is  decanted  and  the  precipitate 
washed  with  hot  water,  ignited,  and  weighed. 


SILVER 

This  metal  is  also  usually  estimated  by  fire  assay,  but  it  may 
be  determined  gravimetrically  as  chloride,  and  (perhaps  more 
accurately)  by  various  well-known  volumetric  methods.  (See 
Part  VII.) 

1.  When   the   sample   has   been   attacked   with   aqua   regia, 
the  silver,  after  diluting  and  settling,  remains  for  the  most  part 
as  insoluble  chloride,  possibly  mixed  with  silica,  carbon,  or  other 
refractory  matter.     The  residue  from  the  aqua  regia  treatment 
is  washed  thoroughly  by  decantation,   dissolved  in  dilute   am- 
monia, filtered,  and  the  filtrate  boiled  and  re-precipitated  with 
a  few  drops  of  HC1,  avoiding  a  large  excess.     After  settling,  the 
AgCl  is  collected  in  a  weighed  porcelain  crucible,  dried,  heated 
to  incipient  fusion,  and  weighed  with  the  crucible. 

2.  In  cases  where  the  sample  has  been  dissolved  in  nitric 
acid,  the  liquid  is  heated  to  boiling  and  the  silver  precipitated 
by  adding  a  slight  excess  of  HC1.     It  is  then  washed,  as  much 
as  possible  by  decantation,  with   boiling  water,  and  treated  as 


ANALYSIS   OF   BULLION  AND   METALLIC   PRODUCTS    433 

above,  except  that  in  this  case  it  is  unnecessary  to  dissolve  in 
ammonia. 

3.  Some  account  of  the  volumetric  methods  of  Gay-Lussac 
and  Volhard  is  given  in  Part  VII.     In  connection  with  the  lat- 
ter, the  writer  is  accustomed  to  use  the  following  procedure.     In 
samples  consisting  chiefly  of  silver,  not  more  than  0.2  gram  need 
be  taken  for  the  estimation.     This  is  dissolved  in  nitric  acid, 
well   boiled,    and   cooled.     The   standard   thiocyanate   is   added 
in  slight  excess;  the  excess  is  then  removed  by  addition  of  a  silver 
solution  equivalent  in  strength  to  one-fifth  that  of  the  thiocyanate, 
until  the  red  color  of  the  ferric  thiocyanate  just  disappears. 

4.  Where  silver  has  been  precipitated  as  chloride,  and  the 
quantity  is  considerable,  it  may  be  determined  volumetrically 
by  the  method  of  Deniges.     The  AgCl  is  dissolved  in  excess  of  a 
standard  solution  of  cyanide,  using  a  measured  quantity  of  the 
latter.     If  the  last  portions  of  the  precipitate  dissolve  with  diffi- 
culty, the  liquid  may  be  poured  off  and  the  residue  dissolved  in 
ammonia,  the  solution  so  formed  being  added  to  the  bulk.    Potas- 
sium iodide  is  now  added,  and  the  residual  cyanide  titrated  with 
standard  AgNO3.     The  reactions  are: 

(a)  AgCl  +  2KCN  =  KAg(CN)2  +  KC1. 
(6)  AgNO3  +  KI     =  Agl  +  KNO3. 
(c)  Agl  +  2KCN     =  KAg(CN)2  +  Kl. 

ESTIMATION  OF  BASE  METALS 

These  may  .generally  be  determined,  after  separation  of  the 
gold  and  silver,  by  the  methods  described  in  Section  I. 

Lead.  —  In  cases  where  selenium  or  tellurium  is  present,  the 
writer  has  found  it  desirable  to  separate  these  elements  as 
described  below,  before  proceeding  to  precipitate  the  lead.  After 
removal  of  these  elements  the  filtrate,  containing  the  lead  as 
chloride  (extracted  by  boiling  water),  is  evaporated  to  a  small 
bulk,  sulphuric  acid  is  then  added,  and  the  liquid  boiled  till 
strong  white  fumes  are  given  off.  It  is  then  cooled,  diluted,  and 
treated  as  described  in  Section  I. 

Copper  is  determined  in  the  filtrate  from  the  lead,  as  already 
described;  the  method  to  be  selected  will  depend  on  the  quan- 
tity present. 

Iron  is  generally  present  in  very  small  amounts  (except  in 
the  case  of  zinc-box  precipitates,  where  it  may  exist  as  ferro- 


434  THE  CYANIDE  HANDBOOK 

cyanides:  see  below).  It  is  generally  estimated  by  the  colori- 
metric  method.  (See  Section  I.) 

Zinc  is  determined  in  the  filtrate  from  iron,  as  described 
above.  (See  Section  I.) 

Calcium.  The  sample  is  boiled  with  HC1  or  in  some  cases 
with  HC1  +  HNO3,  adding  a  considerable  excess  of  HC1.  Dilute 
and  make  alkaline  with  ammonia.  In  presence  of  manganese, 
add  bromine  water.  Boil,  filter,  and  wash  with  hot  water.  Re- 
dissolve  residue  in  HC1  and  re-precipitate  with  ammonia,  adding 
the  second  filtrate  to  the  first.  Heat  filtrate  to  boiling,  add 
excess  of  hot  concentrated  ammonium  oxalate,  and  proceed  as 
described  in  Section  I. 

Manganese,  alumina,  magnesium,  alkali  metals,  etc.  — •  The 
methods  given  in  Section  I  may  be  applied,  having  regard  to  the 
special  circumstances  in  each  case. 

NON-METALS  AND  NEGATIVE  RADICALS 

Sulphur.  —  In  general,  the  sample  should  be  first  dissolved 
in  nitric  acid.  Fusion  with  niter  in  platinum  vessels  is  usually 
inadmissible  with  metallic  samples.  In  cases  where  HNO3  can- 
not be  used,  dissolve  the  sample  in  HC1  +  KC103,  evaporate  and 
boil  with  HC1  till  all  free  chlorine  is  expelled,  dilute,  filter,  heat 
to  boiling,  and  precipitate  with  BaCl2.  Any  gold  which  may 
possibly  remain  in  solution  and  be  carried  down  by  the  BaSO4 
precipitate  may  be  determined,  after  weighing  the  latter,  by 
scorifying  and  cupeling,  and  a  correction  applied  in  calculating 
the  sulphur. 

Selenium  and  tellurium  may  occasionally  be  present  in  quite 
considerable  amounts  in  mattes,  zinc-gold  precipitate,  etc.,  and 
are  tenaciously  retained  by  gold  and  silver  bullion  even  after 
careful  refining.  They  may  be  separated  and  estimated  by  the 
methods  given  in  Section  I. 

Minute  quantities  of  carbon,  silicon,  and  other  elements 
may  be  found  in  the  residue  insoluble  in  aqua  regia,  after  treat- 
ment of  the  latter  with  ammonia  and  ammonium  acetate. 

Cyanogen.  —  1.  In  most  cases,  the  total  cyanogen  may  be  esti- 
mated by  adding  caustic  alkali  and  mercuric  oxide,  and  boiling 
for  some  time.  The  cyanogen  compounds  are  decomposed  and 
yield  soluble  mercuric  cyanide,  HgCy2,  which  unites  with  the 
alkali,  forming  a  double  cyanide,  such  as  Na2HgCy4.  Filter  and 


ANALYSIS   OF   BULLION  AND   METALLIC   PRODUCTS     435 

treat  while  hot  with  H2S  or  Na2S  to  remove  excess  of  mercury. 
The  excess  of  sulphide  is  removed  by  agitation  with  lead  carbon- 
ate. Filter,  add  potassium  iodide,  and  titrate  the  cyanogen 
with  standard  silver  nitrate. 

2.  Proceed  as  above  until  the  double  cyanide  of  mercury  is 
obtained.     Then  add  zinc  nitrate  dissolved  in  ammonia; l  pass 
in  H2S  slowly  until  a  white  precipitate  (ZnS)  begins  to  appear. 
Filter,  add  KI,  and  titrate  with  silver  nitrate. 

3.  A  weighed  portion  of  the  substance  is  mixed  with  about 
four  times  its  weight  of  granulated  zinc,  and  distilled  with  dilute 
sulphuric  acid.     The  mixture  of  hydrogen  and  hydrocyanic  acid 
which  is  given  off  is  led  through  one  or  more  bulbed  U-tubes 
containing  7  per  cent,  silver  nitrate  or  (perhaps  better)  caustic 
alkali.     Boil  for  a  few  minutes  at  the  end  of  the  distillation. 
Sulphuric  acid,  75  per  cent,  by  volume,  may  be  used  instead  of 
zinc  and  dilute  acid.     If  the  HCN  has  been  collected  in  silver 
nitrate,  the  silver  cyanide  is  filtered  off,  ignited,  and  the  residual 
silver  weighed.     If  collected  in  caustic  alkali,  the  tubes  are  washed 
out  into  a  flask,  a  little  KI  added,  and  the  cyanogen. titrated  with 
silver  nitrate. 

Ferrocyanides.  —  1.  In  cases  where  all  the  iron  is  present  as 
ferrocyanide,  it  is  sufficient  to  decompose  the  sample  by  any 
method  which  will  completely  destroy  or  expel  the  cyanogen 
and  estimate  the  iron  in  the  residue.  This  decomposition  may 
generally  be  carried  out  by  boiling  down  with  nitric  acid,  adding 
H2SO4  towards  the  finish,  and  heating  till  white  fumes  are  freely 
given  off.  In  some  cases,  where  the  amount  of  ferrocyanide  is 
small,  it  is  sufficient  to  boil  with  HC1  and  KC1O3,  without  evapo- 
rating to  a  small  bulk. 

2.  E.  Donath  and  B.  M.  Margoshes  2  give  a  method  depend- 
ing on  the  action  of  bromiriized  caustic  soda,  which  is  applicable 
in  cases  where  part  of  the  iron  is  present  in  other  forms  than 
ferrocyanide.  The  substance  is  first  digested  with  8  per  cent, 
caustic  soda  until  as  much  as  possible  is  dissolved,  with  gentle 
warming.  The  whole,  or  an  aliquot  part,  is  then  filtered,  and 
the  filtrate  treated  with  "brominized  caustic  soda,"  prepared  by 
adding  20  cc.  of  bromine  to  a  little  of  the  8  per  cent,  caustic 
soda.  A  precipitate  of  ferric  hydrate  is  thus  obtained,  repre- 

1  Fresenius,  "Quantitative  Analysis,"  Vol.  I,  p.  376  (7th  edition). 
»  "  Journ.  fur  prakt.  Chem.,"  LV  (1899). 


436  THE  CYANIDE  HANDBOOK 

senting  only  that  part  of  the  iron  which  was  originally  present 
as  ferrocyanide.  This  is  filtered  off,  dissolved  in  HC1,  and  re- 
precipitated  with  ammonia.  Its  iron  contents  may  then  be 
determined  by  any  convenient  method.  (See  Section  I.) 

Fe  X  7.56  =  K4FeCy6.3H2O. 


SECTION  III 

ANALYSIS    OF    CYANIDE    SOLUTIONS    AFTER    USE    IN 
ORE  TREATMENT 

IN  general  only  a  few  simple  chemical  tests  have  to  be  made 
on  these  solutions  for  the  purpose  of  regulating  the  daily  work 
of  the  plant;  but  there  are  cases  where  a  complete  analysis  may 
be  desirable  or  necessary;  we  therefore  give  an  outline  of  the 
various  estimations  which  might  be  required.  A  detailed  dis- 
cussion of  this  matter  will  be  found  in  the  present  writer's  "  Chem- 
istry of  Cyanide  Solutions  resulting  from  the  Treatment  of  Ores."  i 

The  following  list  includes  all  the  determinations  which  would 
be  at  all  likely  to  occur  in  such  an  investigation,  though  of  course 
many  of  the  ingredients  enumerated  would  be  absent  in  any 
particular  case. 

(a)  Cyanogen    Compounds.  —  Free    cyanide,    Total    cyanide, 
Total  cyanogen,  Hydrocyanic  acid,  Cyanates,  Cyanurates,  Haloid 
cyanides,    Ferrocyanides,    Ferricyanides,    Thiocyanates,    Seleno- 
cyanates,  Tellurocyanates  (?). 

(b)  Metals.  —  The  most  important  in  the  present  connection 
are:   Gold,    Silver,   Calcium,   Copper,    Iron,    Zinc.     Others   that 
may    sometimes  -  occur    are:    Aluminium,    Antimony,    Arsenic, 
Barium,   Bismuth,   Cadmium,   Cobalt,   Lead,   Magnesium,   Man- 
ganese, Mercury,  Nickel,  Potassium,  Sodium,  Strontium,  Tin. 

(c)  Acid  Radicals  other  than  Cyanogen  Compounds.  —  Bicar- 
bonates,    Bromides,    Carbonates,    Chlorides,    Nitrates,    Nitrites, 
Phosphates,   Silicates,  Sulphates,  Sulphides,  Tellurides,  Thiosul- 
phates. 

(d)  Determinations  of  Alkalinity.  —  "  Protective  "  alkali,  Total 
alkali,  Alkaline  hydrates,  Ammonia. 

(e)  Organic     Matter     (excluding     cyanogen) .  —  Among     the 
substances   noted   by   various  writers  as   occurring  in   cyanide 
solutions    may   be  mentioned:  Azulmates,    Formates,  Oxalates, 
Oxamide,  Urea. 

t  "Eng.  and  Min.  Journ"  (1904). 
437 


438  THE  CYANIDE  HANDBOOK 

(/)  Special  Tests.  —  Insoluble  suspended  matter;  total  dis- 
solved solids;  total  reducing  power;  solvent  activity. 

Only  a  few  of  these  determinations  can  be  described  here, 
and  where  several  methods  are  in  use  for  the  same  substance,  the 
one  given  is  that  which,  in  the  writer's  opinion,  is  of  most  value 
to  the  cyanide  worker. 

TESTS  USED  IN  DAILY  ROUTINE  OF  CYANIDE  PLANT 

These  are  of  the  simplest  description,  and  generally  include 
only:  (a)  Determinations  of  free  cyanide  in  the  solutions  enter- 
ing and  leaving  the  precipitation  boxes,  or  in  the  sumps  and 
storage  tanks,  before  and  after  making  up  to  required  strength, 
with  occasional  special  tests  in  addition  to  these.  (6)  Determina- 
tions of  "protective"  alkali  (i.e.,  of  the  alkalinity  of  the  solu- 
tion, exclusive  of  that  due  to  the  cyanide  itself.)  (c)  Assays  of 
gold  (and  silver,  if  necessary)  in  the  solutions  entering  and  leav- 
ing the  precipitation  boxes.  These  are  described  below,  under 
METALS. 

WORKING  TEST  FOR  FREE  CYANIDE 

From  10  to  50  cc.  of  the  solution,  according  to  its  strength  in 
cyanide,  are  mixed  with  a  few  drops  of  a  strong  solution  of  potas- 
sium iodide  and  titrated  with  a  solution  of  silver  nitrate,  adjusted 
to  give  the  result  with  little  or  no  calculation.  A  strength  com- 
monly used  is  13.04  grams  AgNO3  per  liter,  in  which  case  1  cc. 
=  0.01  gram  KCN  or  0.004  gram  CN.  The  finishing  point  is 
usually  taken  as  the  first  appearance  of  a  permanent  yellowish 
turbidity,  disregarding  a  slight  white  cloudiness  which  may 
appear  earlier.  This  probably  gives  slightly  too  high  a  result  in 
presence  of  K2ZnCy4  and  its  analogues,  as  some  of  the  cyanogen 
of  these  compounds  may  be  also  indicated  when  free  alkali  is 
present.  This  is  not,  however,  of  much  consequence  if  the  test 
be  made  in  the  same  manner  for  all  solutions.  In  absence  of  KI 
the  end-point  (white  turbidity)  is  reached  sooner,  but  is  generally 
uncertain  and  indefinite.  An  intermediate  result,  and  one 
which,  so  far  as  tested,  appears  to  correspond  with  the  actual 
working  strength  of  the  solution,  is  obtained  by  neutralizing 
the  protective  alkali  (as  described  below),  and  then  adding  KI 
and  titrating  with  AgNO3  in  the  usual  way,  taking  as  the  end- 
point  the  appearance  of  a  distinct  permanent  white  turbidity. 


ANALYSIS   OF  CYANIDE  SOLUTIONS  439 

In  making  the  free  cyanide  test  it  is  essential  to  have  the  solu- 
tion to  be  tested  perfectly  clear.  It  must  be  filtered,  if  neces- 
sary, but  the  addition  of  lime  or  other  substance  for  clarifying  is 
generally  not  admissible.  Dilution,  addition  of  alkalis,  varia- 
tion of  temperature  and  other  conditions,  must  also  be  avoided, 
as  all  these  affect  the  reading  given  by  AgNO3,  at  least  in  pres- 
ence of  zinc.  The  tests  should  be  made  in  perfectly  clean  flasks 
and  the  reaction  observed  in  a  good  light  against  a  dark  back- 
ground, as  the  first  turbidity,  which  marks  the  end-point,  is  some- 
what faint.  The  result  may  be  calculated  in  percentage,  or  in 
pounds,  or  kilos  per  ton,  as  desired.  If  10  cc.  of  the  solution  to 
be  examined  has  been  taken,  every  cc.  of  AgNO3  (13.04  grams 
per  liter)  added  will  represent: 

0.1.  per  cent.  KCN  or  0.04  per  cent  CN, 

2  Ib.  KCN  or  0.8  Ib.  CN  per  ton  of  2000  lb., 

1  kg.  KCN  or  0.4  kg.  CN  per  metric  ton  of  1000  kg. 

WORKING   TEST    FOR    PROTECTIVE    ALKALI 

In  absence  of  zinc,  add  to  a  measured  volume  of  the  solution 
to  be  tested  sufficient  silver  nitrate  to  give  a  slight  permanent 
turbidity;  then  without  filtering  add  a  few  drops  of  an  alcoholic 
0.5  per  cent,  solution  of  phenol-phthalein,  and  titrate  with  stand- 
ard acid  until  the  pink  color  just  disappears.  The  amount  of 
standard  acid  used  measures  the  protective  alkali. 

In  presence  of  zinc,  before  titrating  with  acid,  add  a  suf- 
ficient excess  (say  10  cc.)  of  a  5  per  cent,  solution  of  potassium 
ferrocyanide,  and  proceed  exactly  as  above.  The  addition  of 
ferrocyanide  liberates  the  alkali,  which  would  otherwise  be 
precipitated  as  zinc  hydrate  or  carbonate  on  addition  of  silver 
nitrate,  the  reaction  being  probably  somewhat  as  follows: 

(a)  K2ZnCy4  +  2KOH  +  2AgNO3  =  Zn(OH)2  +  2KAgCy2  +  2KNO3. 
(6)  2Zn(OH)2  +  K,FeCy8  =  Zn^eCyr,  +  4KOH. 


with  analogous  reactions  in  the  case  of  carbonates.  In  some 
cases  difficulties  arise  owing  to  the  gradual  return  of  the  phenol- 
phthalein  color  on  standing.  This  may  be  due  to  insufficient 
AgNO3  or  ferrocyanide  having  been  added,  and  may  generally 
be  avoided  by  adding  the  required  amount  of  AgNO3  to  pre- 
cipitate all  the  cyanogen  as  AgCN,  adding  an  excess  of  ferro- 
cyanide and  filtering  before  titrating  the  alkali.  Any  mineral 


440  THE  CYANIDE  HANDBOOK 

acid  (HC1,  HN03,  or  H2SO4)  or  oxalic  acid  (C2H2O4 .  2H20)  may 
be  used  for  the  standard  solution.  It  is  frequently  adjusted  so 
as  to  give  the  alkalinity  in  terms  of  NaOH  or  CaO  without  cal- 
culation. Thus,  a  solution  of  oxalic  acid  containing  1.575  grams 
of  the  crystallized  acid  per  liter  may  be  prepared;  in  this  case 
1  cc.  of  acid  =  0.001  gram  NaOH. 

ESTIMATION  OF  CYANOGEN  COMPOUNDS 

(1)  Free  cyanide.     (See  above.) 

(2)  Total  cyanide,  defined  as  "  the  equivalent  in  terms  of  potas- 
sium cyanide,  of  all  the  cyanogen  existing  as  simple  cyanides 
and   easily   decomposable   double   cyanides,   such   as   K2ZnCy4" 
(excluding   such    bodies    as    KAuCy2,    HgCy2,    K4FeCy6,    KCyS, 
etc.).     It   is   determined   by  making  the  solution   to   be  tested 
strongly  alkaline  (e.g.,  with  caustic  soda),  adding  KI  and  titrat- 
ing the  cyanide  with  AgNO3  to  the  appearance  of  a  permanent 
yellow  turbidity.     For  50  cc.  of  the  solution  to  be  tested,  it  is 
usually  sufficient  to  add  10  cc.  of  an  indicator  containing  4  per 
cent.  NaOH  and  1  per  cent.  KI.     The  following  equation  may 
be  taken  as  representing  the  decomposition  of  zinc  double  cyan- 
ide in  presence  of  excess  of  alkali  and  silver  nitrate:     (Compare 
equation  a,  above.) 

(c)  K2ZnCy4  +  4KOH  +  2AgNO3  =  Zn(OK)2  +  2KAgCy2  +  2KNO3  + 

2H20. 

Total  Cyanogen.  —  The  best  method  of  determining  the  whole 
of  the  cyanogen  present  in  a  solution  appears  to  be  to  boil 
with  oxide  of  mercury  in  excess,  filter,  and  remove  mercury  by 
treatment  with  an  alkaline  sulphide.  Any  excess  of  sulphide  is 
removed  by  agitating  with  lead  carbonate,  added  in  small  quan- 
tities at  a  time,  and  filtering.  The  clear  liquid,  after  addition 
of  KI,  is  titrated  for  cyanide  in  the  ordinary  way  with  AgNO3. 
By  the  above  treatment  practically  all  cyanogen  compounds  are 
converted  into  HgCy2,  which  is  subsequently  decomposed  thus: 

HgCy2  +  Na2S  =  HgS  +  2NaCy. 
(See  also  Section  II  above.) 

Hydrocyanic  Acid.  —  Add  sufficient  AgNO3  to  convert  free 
cyanides  into  double  silver  salts;  in  presence  of  zinc,  add  also 
an  excess  of  ferrocyanide.  The  solution  will  now  appear  acid  to 


ANALYSIS   OF  CYANIDE  SOLUTIONS  441 

phenol-phthalein,  and  the  amount  of  HCy  present  may  be  deter- 
mined by  titrating  this  acidity  with  standard  alkali  solution: 

Ice.  ^  alkali  =  0.0027  gram  HCy. 

Cyanates.  —  These,  if  present  at  all,  would  probably  be 
rapidly  decomposed  under  working  conditions.  (See  Section  IV.) 

Cyanurates.  —  See  "  Notes  on  Residual  Cyanide  Solutions," 
by  Chas.  J.  Ellis.1 

Haloid  Cyanides.  —  Bromide  of  cyanogen,  as  used  in  the 
Sulman  Teed  and  Diehl  processes  (see  Part  VI),  is  determined 
as  follows:  The  solution  is  acidulated  with  HC1  and  KI  added. 
Iodine  is  liberated  as  follows: 

BrCy  +  HC1  +  2KI  =  HCy  +  KC1  +  KBr  +  I2. 

The  iodine  is  estimated  in  the  usual  way  by  titration  with 
standard  thiosulphate : 

N 
Ice.  TQ  iodine  =  0.0053  gram  BrCy. 

The  presence  of  alkali  cyanides  does  not  interfere,  as  they  are 
converted  by  the  HC1  into  HCy,  which  does  not  affect  the  reac- 
tion. 

Ferrocyanides.  —  1.  In  cases  where  all  the  iron  in  the  solution 
exists  in  the  form  of  ferrocyanide,  the  latter  is  best  estimated 
by  determining  the  total  iron,  after  decomposition  of  the  cyan- 
ogen compounds.  This  may  be  done  in  some  cases  by  simply 
adding  a  powerful  oxidizer,  such  as  bromine  or  HC1  -f  KC1O3, 
and  boiling  for  a  few  minutes.  The  iron  may  then  be  completely 
precipitated  by  adding  a  slight  excess  of  ammonia  to  the  hot 
solution,  filtering,  and  determining  iron  by  any  suitable  method. 
(See  Section  I.) 

2.  Where  much  ferrocyanide  is  present  it  will  generally  be 
necessary  to  evaporate  with  HNO3  and  H2SO4,  sometimes  more 
than  once,  until  the  liquid,  made  alkaline  and  re-acidified  with 
HC1,  no  longer  shows  a  trace  of  blue  color.     The  iron  is  then 
separated  and  estimated  as  above. 

3.  Where  other  soluble   compounds  of  iron,   such  as  ferri- 
cyanides  and  nitroprussides,  are  present,  it  is  perhaps  best  to 
determine  the  total  FeCy6,  and  to  estimate  the  amount  of  the 

1  "Journ.  Soc.  Chern.  Ind.,"  February,  1897. 


442  THE  CYANIDE  HANDBOOK 

ferricyanides  etc.,  in  a  separate  portion,  the  ferrocyanide  being 
thus  found  by  difference. 

4.  Where  insoluble  iron  compounds  exist  in  suspension  and 
cannot  readily  be  removed  by  nitration,  the  solution  may  be 
agitated  with  lime  and  filtered,  leaving  the  soluble  cyanogen 
compounds  unaffected.  If,  however,  the  suspended  matter 
itself  contain  insoluble  ferrocyanogen  compounds,  they  will  be 
wholly  or  partially  decomposed  and  a  further  quantity  of  ferro- 
cyanogen added  to  the  solution.  In  many  cases  the  method  of 
Donath  and  Margoshes  may  be  applied.  (See  Section  II.) 

Ferricyanides.  —  In  the  absence  of  other  substances  capable 
of  liberating  iodine  from  potassium  iodide,  ferricyanides  may  be 
estimated  by  the  method  of  Lenssen  and  Mohr.1  After  adding 
KI  and  acidulating  with  HC1,  add  excess  of  zinc  sulphate,  allow 
to  stand  some  time,  and  neutralize  with  NaHCO3.  The  liberated 
iodine  is  then  titrated  with  thiosulphate  in  the  ordinary  way. 

Ice.  —  thiosulphate  =  0.032941  gram  K3FeCyfi. 

Thiocyanates.  —  These  are  most  simply  estimated  by  the  colo- 
rimetric  method,  merely  reversing  the  procedure  for  estimating 
small  quantities  of  iron.  (See  Section  I.)  The  solution  is  acidified 
with  HC1  and  filtered.  An  excess  of  ferric  chloride  or  nitrate  is 
then  added,  and  the  color  compared  with  that  of  a  similar  amount 
of  ferric  solution  and  HC1  diluted  to  a  similar  volume,  to  which 
standard  KCyS  is  added  until  the  tints  are  alike. 

Selenocyanides  and  Tellurocyanides.  —  Selenium  dissolves  pretty 
readily  in  cyanide,  forming  compounds  analogous  in  com- 
position to  thiocyanates.  Tellurium  is  less  easily  dissolved,  and 
may  possibly  be  present  as  telluride,  tellurite,  or  tellurate  of  an 
alkali  metal.  The  estimation  is  made  as  described  below,  under 
Selenium  and  Tellurium. 

ESTIMATION  OF  METALS 

In  most  cases  these  estimations  are  made,  after  decomposi- 
tion of  the  cyanogen  compounds,  by  the  methods  already  de- 
scribed in  Sections  I  and  II.  There  are,  however,  certain  special 
methods  applicable  to  cyanide  solutions  which  must  be  described. 

1  Sutton,  "Volumetric  Analysis,"  8th  edition,  p.  227. 


ANALYSIS   OF  CYANIDE  SOLUTIONS  443 


GOLD 

1.  The  standard  method  is  that  of  evaporation  with  litharge. 
A  measured  quantity  of  the  solution,  usually  not  more  than 
300  cc.,  is  placed  in  a  porcelain  evaporating  dish.  Litharge 
(20  to  50  grams)  is  then  sprinkled  over  the  surface  of  the  liquid 
and  the  mixture  allowed  to  evaporate  at  a  gentle  heat,  without 
boiling.  The  evaporated  residue  is  then  fluxed  as  an  ordinary  ore 
assay.1 

2  Of  the  numerous  alternative  methods  that  have  been  pro- 
posed, perhaps  the  best  is  that  suggested  originally,  about  1896, 
by  S.  B.  Christy.2  It  consists  in  acidulating  the  solution  and 
adding  a  copper  salt  together  with  a  reducing  agent,  such  as  a 
soluble  sulphite,  whereby  a  precipitate  of  cuprous  cyanide  is 
formed  which  carries  down  all  but  a  minute  trace  of  the  gold.  It 
was  at  first  considered  necessary  to  heat  the  solution  after  adding 
acid,  to  expel  the  bulk  of  the  HCy,  but  A.  Whitby  3  has  shown 
that  the  reaction  is  complete  in  the  cold ;  he  adds,  first,  a  sufficient 
volume  of  10  per  cent,  copper  sulphate,  then  a  few  cc.  cone. 
HC1.  and  finally  10  to  20  cc.  of  10  per  cent,  sodium  sulphite. 
After  vigorous  stirring  and  settling,  the  precipitate  is  filtered 
off,  and  the  necessary  flux  added  to  the  filter-paper.  The  whole 
is  then  transferred,  without  drying,  to  a.  small  clay  crucible  and 
fused  like  an  ordinary  assay.  Both  gold  and  silver  are  precipi- 
tated together  and  can  be  determined  in  the  same  assay;  the 
method  has  the  advantage  that  no  heat  is  required  in  the 
preliminary  operations.  The  writer  has  employed  this  method, 
using  the  following  proportions: 

Solution  to  be  tested:  10  a.  t.  =  291  §cc. 

Copper  sulphate  (10  percent.  CuSO4  •  5H2O) 20cc. 

Sodium  sulphite  (15  per  cent.  Na2SOa)    20cc. 

Sulphuric  acid  (10  per  cent.  H2SO4) lOcc. 

These  are  added  in  succession,  stirring  after  each  addition. 
A  little  ferrocyanide  added  to  the  solution  promotes  settlement. 
After  thorough  stirring,  the  mixture  is  allowed  to  settle  about 
fifteen  minutes,  filtered  in  a  large  paper,  and  the  filtrate  passed 
back  through  the  funnel  once  or  twice  until  quite  clear.  No 

1  For  details,  see  "Chemistry  of  Cyanide  Solutions,"  p.  114. 

2  "Trans.  A.  I.  M.  E."  (1896),  pp  1-38;  "Min.  Sci.  Press,"  Dec.  19,  1896. 

3  "Proc.  Chem.,  Met.  and  Min.  SOP     f  S.  A.,"  Ill,  15. 


444  THE  CYANIDE  HANDBOOK 

water-wash  is  necessary.  When  the  precipitate  is  sufficiently 
drained,  60  grams  of  the  following  flux  are  placed  on  the  same 
filter:  Borax,  30  parts;  litharge,  30  parts;  charcoal,  1  part. 

The  paper  is  then  immediately  wrapped  over  the  flux  and  pre- 
cipitate and  the  whole  placed  in  a  hot  E  or  F  clay  crucible,  fused, 
and  cupeled. 

3.  H.  T.  Durant 1  gives  a  method  which,  with  various  modi- 
fications,  has   been   adopted   by   many   cyanide   workers.     The 
solution  is  acidulated  with  H2SO4  and  boiled.     About  5  grams 
of  zinc  shavings  are  then  added,  in  quantities  of  about  1  gram  at 
a  time.     More  acid  is  added  if  required,  and  the  boiling  continued 
till  the  zinc  is  apparently  dissolved.     Remove  from  the  heat  and 
add  lead  acetate  to  form  lead  sulphate,  which  collects  the  gold. 
Filter  through  a  double  filter-paper.     If  the  action  is  slow,  owing 
to  the  zinc  being  very  pure,  add  a  few  drops  of  copper  sulphate 
at  the  beginning.     The  filter,  with  the  precipitate,  is  placed  on  a 
layer  of  borax  in  a  scorifier,  allowed  to  dry,  and  char  slowly  in 
front   of   a  muffle,  then  scorified  with  lead  and  cupeled  in  the 
usual  way. 

A  slight  modification  of  this  method  is  given  by  N.  S.  Stines,2 
as  follows:  100  cc.  of  the  solution  are  mixed  with  7  cc.  of  a  10 
per  cent,  lead  acetate  solution  and  1  gram  zinc  shavings.  Heat, 
without  boiling,  for  say  twenty-five  minutes.  Add  20  cc.  HC1 
and  heat  till  effervescence  stops.  "The  lead  is  then  in  such  a 
spongy  condition  that  by  the  aid  of  a  flattened  glass  rod  it  can 
be  pressed  into  a  cake  and  the  clear  solution  poured  off."  Transfer 
the  mass  to  a  lead-foil  funnel,  place  in  a  hot  cupel,  and  complete 
the  assay  as  usual. 

4.  Where  large  numbers  of  assays  have  to  be  made  simul- 
taneously, perhaps  the  simplest  and  least  troublesome  method 
is  to  evaporate  the  solution,  without  boiling,  in  a  dish  or  other 
vessel  of  lead  foil;  when  dry,  the  whole  is  scorified  and  cupeled. 
For  single  assays  the  method  is  rather  slow. 

5.  A  number  of  colorimetric  methods  have  been  suggested 
for  the  rapid  approximate  determination  of  gold  in  cyanide  solu- 
tions, all  depending  on  the  oxidation  of  the  cyanide  by  some 
powerful  reagent,   and  subsequent   addition    of    stannous    chlo- 

1  Private  communication  to  the  author. 
a  "Min.  Sci.  Press,"  April  28,  1906. 


ANALYSIS   OF  CYANIDE  SOLUTIONS  445 

ride  to  the  acidulated  solution  to  obtain  the  purple  of  Cassius 
color. 

(a)  In  Cassel's  method,1  which  is  the  simplest,  the  prelim- 
inary oxidation  is  obtained  with  potassium  bromate  and  sul- 
phuric  acid,   or  with  HC1  +  KC1O3,   KBr  +  Na2O2,   or  KBr  + 
K2O2.     The  procedure  is  as  follows:  Mix  10  to  50  cc.  of  the  solu- 
tion to  be  tested  with  0.5  gram  KBrO3  and  add  concentrated 
H2SO4  gradually,  with  shaking,  till  the  reaction  starts.     When 
the  action  ceases,  add  drop  by  drop  a  saturated  solution  of  SnCl2 
till  the  liquid  is  just  colorless.     The  purple  color  now  begins  to 
develop  and  is  most  intense  after  about  half  a  minute.     The 
color  is  compared  with  that  given  by  a  standard  gold  solution 
under  similar  conditions. 

(b)  In  J.   Moir's  method,2   100  cc.  of  solution  are  oxidized 
with  1  to  2  grams  Na2O2  and  boiled.     A  few  drops  of  lead  acetate 
are  added,  which  produce  a  brown  spot  of  PbO2.     This  re-dis- 
solves immediately  if  sufficient  Na2O2  is  present.     A  small  quan- 
tity of  aluminium  powder  is  now  added,  and  a  Pb  =  Al  couple 
forms  which  throws  down  the  gold.     The  mixture  is  filtered  and 
the  filtrate  rejected.     The  residue  on  the  filter  is  dissolved  by 
aqua  regia  and  treated  with  SnCl2,  added  drop  by  drop  till  the 
liquid  is   colorless.     Permanent   standards  for  comparison   may 
be  made  by  using  a  mixture  of  copper  sulphate  and  cobalt  nitrate, 
adjusting  the  amounts  of  each  until  the  tint  is  the  same  as  that 
given  by  a  known  amount  of  gold  treated  as  above  described. 
The  purple  of  Gassius  color  fades  on  standing,  owing  to  oxida- 
tion. 

(c)  For  further  modification  of  this  test  by  Prof.  A.  Prister 
(see  "Proc.  Chem.,  Met.  and  Min.  Soc.  of  S.  A.,"  IV,  235,  455, 
1904). 

SILVER 

The  methods  Nos.  1,  2,  and  4  described  under  gold,  serve  also 
for  the  estimation  of  silver.  In  dilute  solution,  the  silver  may 
be  separated,  free  from  gold,  by  precipitating  with  sodium  sul- 
phide after  adding  a  few  drops  of  a  solution  of  some  lead  com- 
pound. The  precipitate  should  be  washed  with  dilute  Na^, 
dried,  scorified,  and  cupeled,  or  it  may  be  converted  into  bro- 

i  "Eng.  and  Min.  Jour.,"  Oct.  31,  1903. 

»  "Proc.  Chem.,  Met.  and  Min.  Soc.  of  S.  A.,"  IV,  298  (September,  1903). 


446  THE  CYANIDE  HANDBOOK 

mide  by  addition  of  bromine,  washed,  dried,  fused,  and  weighed 
as  AgBr. 

CALCIUM 

To  100  cc.  of  the  solution  add  10  cc.  HC1  and  boil  for  ten 
minutes.  Filter,  again  heat  nitrate  to  boiling,  and  make  slightly 
alkaline  with  ammonia.  Filter  if  necessary.  To  the  boiling 
solution  add  10  cc.  cone,  solution  of  ammonium  oxalate,  also 
boiling,  and  stir  thoroughly.  Allow  to  settle  till  clear.  Filter 
and  wash  with  hot  water  till  free  from  soluble  oxalates.  Wash 
precipitate  back  into  original  flask,  add  10  cc.  25  per  cent.  HC1, 
heat  to  boiling,  add  50  cc.  water  and  5  cc.  cone.  H2SO4;  heat  to 

N 
70°  C.,  and  titrate  with  —  permanganate. 

Ice.  =  0.001  gram  Ca  =  0.001  per  cent,  on  lOOcc.  tested. 

The  permanganate  should  be  standardized  on  pure  crystallized 
oxalic  acid,  under  the  same  conditions  as  the  test. 

COPPER 

Boil  with  HC1  +  KC1O3  to  decompose  cyanogen  compounds. 
In  some  cases  it  will  be  necessary  to  evaporate  with  HNO3  + 
H2S04  till  white  fumes  of  S03  are  given  off.  Dilute,  add 
ammonia  in  excess,  boil  and  filter.  Estimate  copper  by 
colorimetric  method.  (See  Section  I.)  When  large  amounts  of 
copper  are  present,  decompose  cyanides  as  above  and  precipitate 
with  H2S  in  hot  dilute  acid  solution.  Determine  copper  in  the 
precipitate  as  described  in  Section  I. 

IRON 

After  decomposing  cyanogen  compounds  by  boiling  with 
acids  and  oxidizers,  as  above,  add  excess  of  ammonia  and  boil. 
Filter;  if  the  precipitate  is  considerable,  re-dissolve  in  HC1  and 
re-precipitate  with  ammonia.  Small  quantities  are  determined 
by  the  colorimetric  test  with  thiocyanate;  larger  amounts  by 
reduction  and  titration  with  KMn04  or  K2Cr2O7.  (See  Section  I.) 

ZINC 

1.  The  solution  is  made  strongly  alkaline  with  caustic  soda, 
heated  to  boiling,  and  Na2S  added  as  long  as  a  precipitate  forms. 


ANALYSIS   OF  CYANIDE  SOLUTIONS  447 

After  settling,  filter  off  the  precipitate,  which  may  contain  Ag, 
Hg,  Pb,  and  Zn,  and  wash  with  hot  dilute  Na2S.  Dissolve  in 
HC1,  boil,  dilute,  and  filter.  Titrate  filtrate  at  70°  with  standard 
ferrocyanide  and  uranium  indicator.  (See  Section  I.) 

2.  Oxidize    cyanogen    compounds    by    boiling   with    HC1  + 
KClOa;  precipitate  copper,  etc.,  with  H2S,  and  determine  zinc  in 
filtrate  by  any  suitable  method. 

3.  Precipitate  zinc  as  sulphide,  as  in  method  No.  1.     Wash 
thoroughly  with  hot  water  till  free  from  soluble  sulphides;  transfer 

N 
precipitate  with  filter-paper  to  a  flask.     Add  —  iodine  in  slight 

excess,  together  with  very  dilute  HC1.  The  following  reaction 
occurs:  ZnS  +  2HC1  +  If  =  ZnCl2  +  2HI  +  s 

Care  must  be  taken  to  exclude  air  as  much  as  possible.  After 
shaking,  and  standing  for  a  few  minutes,  titrate  excess  of  iodine 

N 
with  —  thiosulphate. 


10 


Ice.  —  iodine  or  thiosulphate =0.00327  gram  Zn. 


OTHER   METALS 

The  remaining  metals,  which  are  commonly  of  less  importance 
in  cyanide  solutions,  are  estimated  after  complete  decomposition 
of  cyanogen  compounds  by  the  ordinary  methods  of  analysis. 
(See  Section  I.)  .  Where  volatile  metals,  such  as  As  and  Sb,  are 
to  be  determined,  it  is  best  to  destroy  the  cyanogen  by  an  alkaline 
oxidizer,  such  as  Na202  or  brominized  caustic  soda,  before  acid- 
ulating and  precipitating  with  H2S. 

Mercury  and  lead  may  be  precipitated  direct  from  the  solution 
by  H2S.  Lead,  which  would  in  most  cases  be  present  as  an  alka- 
line plumbate,  is  shown  by  a  white  precipitate  on  addition  of 
sodium  carbonate,  which  may  be  filtered  off  and  dissolved  in 
acetic  acid.  The  metal  is  then  detected  by  the  ordinary  quali- 
tative tests.  It  is  best  estimated  by  boiling  a  portion  of  the 
original  solution  with  HNO3  +  H2SO4  till  white  fumes  are  freely 
given  off,  and  proceeding  as  described  in  Section  I. 

Manganese  may  conveniently  be  estimated  by  the  colori- 
metric  method.  The  solution  is  mixed  with  concentrated  HNO3 
and  boiled  for  some  time;  then  peroxide  of  lead  is  added  and 


448  THE  CYANIDE  HANDBOOK 

the  boiling  continued  for  a  few  moments.  Dilute  to  100  cc. 
and  filter.  Reject  the  first  10  cc.  of  the  filtrate,  collect  50 
cc.  and  compare  the  tint  with  that  of  standard  permanganate 
containing  nitric  acid  and  diluted  to  an  equal  volume.  This 
represents  the  Mn  in  half  the  volume  of  cyanide  solution  taken 
for  the  test. 

ESTIMATION  OF  ACID  RADICALS  (OTHER  THAN  CYANOGEN  COM- 
POUNDS) 

Carbonates.  —  To  100  cc.  of  the  solution  add  10  to  15  cc.  of 
a  neutral  2  per  cent,  solution  of  barium  chloride.  Agitate  and 
allow  to  settle  for  an  hour.  Filter,  passing  the  filtrate  back 
through  the  filter-paper  till  clear.  Wash  thoroughly  with  water 
till  washings  are  free  from  cyanide  and  alkali.  Transfer  paper 

N 
and  precipitate  to  a  flask,  add  a  slight  excess  of  —  acid  (HC1  or 

N 
H2SOJ,  warm  to  90°  C.,  and  titrate  residual  acid  with  —  alkali 

and  methyl  orange. 

Na2CO3  +  BaCl2  =  BaCO3  +  2NaCl. 
BaCO3  +  2HC1     =  BaCl2  +  H2O  +  CO2. 

N 
Ice.  —  acid  =  0.0022  gram  CO2  as  carbonate 

=  0.005305  gram  Na2CO3. 

Bicarbonates.  —  Add  caustic  soda  free  from  carbonates  to 
another  portion  of  the  solution  and  apply  the  test  for  carbonates 
as  above.1  NaOH  +  NaHCo3  =  Na2CO3  +  H2O. 

The  increase  in  the  amount  of  CO2  or  Na2C03  found  as  com- 
pared with  the  previous  test  is  a  measure  of  the  bicarbonate. 

Chlorides.  —  The  methods  usually  given,  in  which  chloride 
and  cyanide  are  precipitated  together  by  means  of  silver  nitrate, 
and  the  cyanide  determined  separately  in  another  portion  of  the 
liquid,  are  unsatisfactory,  because  the  amount  of  chloride  is 
usually  very  small  in  comparison  with  the  cyanide.  The  writer 
has  found  that  the  cyanide  can  be  readily  decomposed  and  ex- 
pelled by  boiling  the  solution  with  ammonium  nitrate  or  sul- 
phate; the  cyanide  is  volatilized  as  ammonium  cyanide: 

(NH4)2SO4  +  2NaCy  =  Na2SO4  +  2NH4Cy. 
1  Gerard  W.  Williams,  "Proc.  Chem.,  Met.  and  Min.  Soc.  of  S.  A.,"  IV,  412. 


ANALYSIS   OF   CYANIDE  SOLUTIONS  449 

leaving  the  chloride  unaffected.  The  solution  can  then  be  acid- 
ified with  HNO3  and  the  chloride  determined  by  adding  a  meas- 
ured quantity  of  AgNO3  solution,  filtering  and  determining 
excess  of  AgNO3  by  titration  with  thiocyanate. 

Nitrates.  —  Probably  the  simplest  method  is  to  precipitate 
cyanogen  compounds  with  excess  of  a  soluble  silver  salt,  such  as 
the  acetate  or  sulphate,  filter  and  determine  nitrates  in  the  fil- 
trate by  distilling  with  caustic  soda  and  a  mixture  of  granulated 
zinc  and  iron  filings.  The  ammonia  evolved  is  collected  in  a 
measured  volume  of  standard  acid  and  the  residual  acid  titrated.1 

N 
Ice.  ^.  acid  consumed  =  0.001401  gram  N  =  0.008506  gram  NaNO3. 

Nitrites.  —  In  absence  of  ferricyanides  and  haloid  cyanogen 

compounds,  these  may  be  determined  by  adding  an  air-free  mix- 

ture of  KI  and  H2S04  and  titrating  the  liberated  iodine  with 

thiosulphate,  care  being  taken  to  exclude  air  during  the  process. 

H2SO4  +  KI  +  KNO2  =  K2SO4  +  NO  +  H2O  +  I. 

Phosphates  and  silicates  may  be  estimated  by  ordinary  methods 
of  analysis  in  the  residue  after  evaporation  with  acids  and  igni- 
tion to  destroy  organic  matter  and  render  silica  insoluble.  (See 
Section  I.) 

Sulphates  are  estimated  by  precipitating  with  BaCl2,  filter- 
ing and  washing  the  precipitate  till  free  from  cyanides,  etc., 
re-dissolving  in  hot  dilute  HC1,  filtering  and  igniting  the  insoluble 
residue  and  weighing  as  BaSO4. 

Sulphides.  —  4.  These  are  present  usually  only  in  very  small 
quantities  and  are  best  estimated  colorimetrically  by  means  of 
a  solution  of  sodium  plumbate  or  alkaline  lead  tartrate,  com- 
paring the  tint  with  that  given  by  a  sodium  sulphide  solution  of 
known  strength,  to  which  an  equal  amount  of  the  lead  solution 
has  been  added.2  If  the  strength  of  the  lead  solution  is  known, 
that  of  the  sulphide  solution  may  be  determined  by  means  of 
it.  A  convenient  method  of  standardizing  the  sodium  sul- 
phide solution  is  to  add  to  a  given  volume  of  it  an  excess  of  a 
solution  of  silver  sodium  cyanide,  filter  off  the  precipitate  of  Ag2S, 
and  titrate  the  liberated  cyanide  with  AgNO3  and  KI  indicator. 
1  gram  KCy  found  =  0.3  gram 


i  Sutton,  "Volumetric  Analysis,"  8th  edition,  p.  274. 
aC.  J.  Ellis,  "Journ.  Soc.  Chem.  Ind.,"  February,  1897. 


450  THE  CYANIDE   HANDBOOK 

2.  The  presence  of  sulphides  in  a  solution  may  be  detected 
by  adding  sodium  nitroprusside,  which  gives  a  characteristic 
purple  color.  A  colorimetric  method  based  on  this  reaction  has 
been  devised  by  Dr.  J.  Loevy,1  but  the  writer  finds  it  less  reliable 
than  that  depending  on  the  coloration  of  lead  solutions. 

Thiosulphates.  —  The  writer  finds  that  thiosulphates  may  be 
accurately  determined  in  presence  of  cyanides  and  thiocyanates 
as  follows:  A  drop  of  methyl  orange  is  added  to  the  solution, 

]y 
and  — •  acid  run  in  till  the  liquid  is  exactly  neutralized.     The 

thiosulphate  is  then  determined  by  titrating  with  a  standard 
solution  of  iodine  in  potassic  iodide,  using  starch  indicator  at 
the  finish.  2Naa&O.  +  I.  =  2NaI  +  Na2S4O6. 

Total  sulphur.  —  By  treating  with  a  powerful  oxidizer,  such 
as  HC1  +  KC103,  sulphides,  thiosulphates,  and  thiocyanates 
are  converted  into  sulphates,  and  may  be  determined,  along  with 
any  sulphates  originally  present,  by  boiling  off  the  excess  of  chlo- 
rine, etc.,  and  precipitating  the  hot  solution  with  barium  chloride. 

Selenium  and  Tellurium.  —  On  heating  a  solution  containing 
selenocyanides  with  excess  of  HC1,  the  selenium  is  thrown  down 
as  a  scarlet  precipitate  (mixed  with  AgCl  and  certain  ferrocyanides 
in  some  cases).  In  absence  of  cupric  ferrocyanide  it  may  be 
estimated  colorimetric  ally  by  comparing  the  tint  obtained  with 
that  given  under  similar  conditions  with  a  standard  solution  of 
sodium  selenite  or,  better,  selenocyanide  containing  a  known 
amount  of  selenium.  The  finely  divided  selenium  remains  in 
suspension  for  a  considerable  time.  In  some  cases  an  exact 
imitation  of  the  tint  is  obtained  by  mixing  varying  amounts  of 
zinc  ferrocyanide  with  the  standards. 

When  both  selenium  and  tellurium  are  present,  the  solution 
is  boiled  for  some  time  with  aqua  regia,  to  form  selenates  and 
tellurates,  filtered,  evaporated  with  addition  of  NaCl  on  a  water- 
bath,  and  the  residue  heated  with  HC1  until  all  HNO3  has  been 
driven  off.  The  solution  is  then  diluted,  heated  to  boiling,  and 
precipitated  with  SO2  gas.  The  precipitate  is  collected  on  a 
weighed  filter,  dried  at  100°  C.,  and  weighed.  It  may  contain 
gold;  for  separation  see  Sections  I  and  II. 

1  "Proc.  Chem.,  Met.  and  Min.  Soc.  of  S.  A.,"  II,  608  (1899);  "Chemistry  of 
Cyanide  Solutions,"  p.  92. 


ANALYSIS   OF  CYANIDE  SOLUTIONS  451 

ALKALI  DETERMINATIONS 

Protective  alkali.  —  See  above,  under  "  Tests  used  in  daily 
routine  of  Cyanide  Plant." 

Total  alkali.  —  This  is  defined  as  the  equivalent  in  terms  of 
NaOH,  of  all  the  substances  which  are  alkaline  to  methyl  orange 
It  is  generally  determined  by  adding  to  a  measured  volume  of 

N 
the  solution  a  known  quantity  of  —  acid  in  excess  of  the  required 

amount,  making  up  to  a  definite  volume  and  titrating  an  aliquot 

N 
part  of  the  solution  with  —  alkali,  using  a  few  drops  of  a  0.1 

per  cent,  aqueous  solution  of  methyl  orange  as  indicator.1 

Alkaline  hydrates.  —  These  may  be  determined  by  titrating 

N 
with  —  acid  and  phenol-phthalein,  after  precipitating  carbonates, 

as  already  described,  with  barium  chloride,  filtering,  and  adding 
silver  nitrate  to  the  filtrate  until  a  permanent  precipitate  is 
obtained.  In  presence  of  zinc  it  is  necessary  also  to  add  a  ferro- 
cyanide.2  The  results  are  not  very  exact,  as  the  BaCO3  generally 
carries  down  some  of  the  hydrate  as  Ba(OH)2. 

Ammonia  and  ammonium  salts.  —  Add  excess  of  AgNO3,  i.e., 
sufficient  to  precipitate  all  cyanogen  compounds,  then  a  little 
NaCl  to  remove  excess  of  AgNOs,  filter,  wash,  evaporate  filtrate 
on  a  water-bath  to  a  moderate  bulk,  distil  with  caustic  soda  or 

sodium  carbonate,  and  collect  distillate  in  —  acid.    (For  appara- 

N 
tus,  see   page  442.)      Titrate  residual  acid  with  —  alkali   and 

methyl  orange.  If  free  ammonia  only  is  to  be  estimated,  use 
water  instead  of  NaOH  or  NajCOg  for  distilling.  In  this  case 
also  the  preliminary  evaporation  on  water-bath  must  of  course  be 
omitted. 

ORGANIC  MATTER  (EXCLUDING  CYANOGEN  COMPOUNDS) 
Many  obscure  organic  compounds  may  occasionally  occur  in 
cyanide  solutions,  particularly  if  the  material  treated  has  been 
mixed  with  decaying  animal  or  vegetable  matter.     These  need 

1  "('hcinistrv  of  Cyanide  Solutions,"   p.  62. 

a  L.  M.  Green,  "Trans.  I.  M.  M.,"  X,  29  (1901). 


452  THE  CYANIDE  HANDBOOK 

not  be  discussed  in  detail.  They  may  generally  be  removed, 
and  a  clear  solution  obtained  by  agitating  with  lime  and  filter- 
ing; this  treatment  does  not  affect  ferrocyanides,  thiocyanates, 
and  similar  bodies.  Among  the  more  usual  forms  of  organic 
matter  resulting  from  the  decomposition  of  cyanide  itself  under 
the  influence  of  alkalis  and  water,  may  be  mentioned  oxalates 
of  the  alkali  metals,  and  urea. 

Oxalates.  —  C.  ,T.  Ellis  *  gives  the  following  method.  The 
solution  to  be  tested  is  precipitated  with  calcium  chloride  in  ex- 
cess. The  precipitate,  after  settling,  is  filtered  off  and  washed, 
and  dissolved  in  a  small  excess  of  hydrochloric  acid.  The  oxalic 
acid  thus  formed  is  then  titrated  in  warm  solution  by  standard 
permanganate: 

5C2H2O4  +  2KMnO4  +  3H2SO4  =  K2SO4  +  2MnSO4  +  10CO2  +  8H2O 
Ice.  ^  permanganate  (3.16  gram  KMnO4  per  liter)  =  0.0044  C2O4  = 
0.0063  gram  C2H2O4  •  2H2O. 

Urea.  —  If  the  distillation  for  ammonia,  described  above  under 
alkali  determinations,  be  carried  out  at  a  moderate  temperature 
without  boiling,  and  without  using  too  large  an  excess  of  alkali, 
the  urea  will  remain  practically  unchanged  in  the  flask  after 
the  operation.2  It  may  be  determined  by  decomposing  the  sub- 
stance with  sodium  hypobromite,  warming  slightly  towards 
the  finish.3  CO(NH2)2  +  3NaBrO  =  3NaBr  +  2H2O  +  CO2  +  N2 

The  nitrogen  evolved  is  collected  and  measured  in  a  suitable 
graduated  tube,  and  the  necessary  corrections  for  temperature 
and  pressure  applied,  the  C02  being  absorbed  by  some  alkaline 
liquid. 

SPECIAL  TESTS 

Solids  in  Suspension.  —  The  solutions  dealt  with  in  cyanide 
work  are  very  frequently  turbid  with  solid  matter  in  suspension, 
and  it  may  become  a  matter  of  importance  to  determine  the 
amount  and  nature  of  this  suspended  matter.  A  measured  vol- 
ume of  the  liquid  is  filtered  through  an  ashless  paper,  previously 
dried  at  100°  C.  and  weighed  in  a  weighing  tube.  The  residue 
collected  on  the  filter  is  washed  free  from  soluble  matter,  dried  at 

1  "Journ.  Soc.  Chem.  Ind.,"  XVI,  115  (February,  1897). 

'  C.  J.  Ellis,  loc.  cit. 

3  Sutton,  "Volumetric  Analysis,"  8th  edition,  p.  432. 


ANALYSIS   OF  CYANIDE  SOLUTIONS  453 

the  same  temperature  as  before,  and  weighed.  The  residue 
may  then  be  calcined  and  examined  by  the  ordinary  methods  of 
analysis.  Generally,  it  consists  chiefly  of  silica  and  compounds 
of  iron,  zinc,  calcium,  etc. 

Total  Dissolved  Solids.  —  A  portion  of  the  liquid  is  filtered  and 
evaporated  to  dryness  in  a  weighed  dish  at  a  low  temperature. 
In  some  cases  decomposition  takes  place  even  at  100°  C.,  and  the 
dry  weight  of  the  solids  can  only  be  obtained  by  evaporating  in 
vacuo.  When  the  residue,  as  is  frequently  the  case,  is  very 
deliquescent,  it  may  be  transferred  when  apparently  dry  from 
the  dish  to  a  weighing-bottle,  left  for  some  time  at  the  required 
temperature,  cooled  in  a  desiccator,  and  weighed  in  the  stoppered 
bottle. 

Reducing  Power.  —  Substances  capable  of  absorbing  oxygen 
are  detrimental  to  the  successful  working  of  the  process.  In  the 
event  of  bad  extractions  it  is  often  useful  to  ascertain  whether 
such  substances  are  present  in  the  solution  in  large  quantity. 
The  test  is  generally  made  by  acidulating  a  measured  quantity 
of  the  solution  with  H2S04  and  running  in  permanganate  of  known 
strength  as  long  as  the  color  disappears.1 

A  better  method  is  to  add  to  the  acidulated  solution  an  excess 
of  permanganate,  and  after  standing  for  some  time  till  the  reac- 
tion is  complete,  to  determine  the  excess  by  adding  KI  and 
titrating  the  liberated  iodine  with  hyposulphite.  Dilute  stand- 

/          N\ 

ard  solutions,  ( say  • —  J   are  preferable  in  most  cases.     Fixed 
\         luO/ 

quantities  of  acid,  solution,  and  permanganate  should  be  used  in 
all  tests.  If  this  determination  be  made  at  regular  intervals, 
any  variation  from  normal  conditions  will  be  at  once  detected. 
Solvent  Activity.  —  The  efficiency  of  a  cyanide  solution  for 
dissolving  gold  obviously  depends  on  a  great  variety  of  circum- 
stances besides  the  strength  of  the  solution  in  free  cyanide,  as, 
for  example,  on  the  time  of  contact,  quantity  of  dissolved  oxygen 
in  the  solution,  temperature,  nature  of  surfaces  in  contact  with 
liquid,  etc.2  The  methods  which  have  been  suggested  for  deter- 
mining what  may  be  termed  the  "  solvent  activity  "  of  a  solution 
generally  depend  on  measuring  the  quantity  of  metal  dissolved 
in  a  given  time  under  given  conditions.  Weighed  pieces  of  gold 

1  See  "Chemistry  of  Cyanide  Solutions,"  p.  70. 

2  "Chemistry  of  Cyanide  Solutions,"  p.  54. 


454  THE  CYANIDE  HANDBOOK 

or  silver  are  suspended  in  the  liquid,  with  or  without  agitation, 
and  weighed  after  a  certain  interval  of  time.  This,  however, 
generally  gives  discordant  results,  owing  to  the  impossibility  of 
securing  uniform  conditions  of  surface,  etc. 

A  more  promising  method  is  to  prepare  equal  quantities  of 
precipitated  gold  in  a  number  of  separate  and  similar  vessels 
by  means  of  gold  chloride  and  sulphurous  acid,  making  faintly 
alkaline  with  caustic  soda  and  adding  to  each  a  fixed  volume  of 
the  various  solutions  to  be  compared.  After  agitating  a  definite 
length  of  time,  the  residual  gold  is  filtered  off,  dried,  cupeled, 
and  weighed.  The  difference  between  this  weight  and  that  of 
the  gold  taken  is  the  measure  of  the  solvent  activity  of  the  solu- 
tion. 


SECTION   IV 

ANALYSIS   OF  COMMERCIAL  CYANIDE 

THE  extensive  and  increasing  use  of  the  cyanides  of  the  alkali 
metals  in  the  extraction  of  gold  and  silver,  and  in  other  indus- 
tries, renders  the  question  of  the  accurate  analysis  of  these  pro- 
ducts one  of  considerable  importance.  The  mere  fact  that  for 
several  years  an  impure  brand  of  sodium  cyanide,  containing 
10  per  cent,  or  more  of  foreign  substances,  was  placed  on  the 
market  as  "98  per  cent,  potassium  cyanide,"  and  was  generally 
regarded  as  the  high-water  mark  of  commercial  excellence  for 
this  product,  ought  to  demonstrate  the  necessity  for  increased 
attention  to  this  matter. 

The  following  are  the  chief  constituents  of  the  ordinary  brands 
of  commercial  cyanide. 

(1)  Acid  Radicals  (generally  in  combination  with  the  alkali 
metals) :    Cyanides,    Carbonates,    Bicarbonates,    Chlorides,   Cya- 
nates,  Ferrocyanides,1  Hydroxides,  Sulphates,1  Sulphides,1  Thio- 
cyanates,1  Thiosulphates,1  Silicates.1 

(2)  Metallic    Radicals.  —  Sodium,     Potassium,     Ammonium, 
Aluminium,1  Calcium,1  Iron,1  Magnesium/  Silver/  Zinc.1 

(3)  Moisture  and  insoluble  matter. 

SAMPLING  AND  PREPARATION 

Cyanide  is  usually  consigned  in  cases  with  air-tight  metallic 
linings,  so  that  on  opening  the  case  it  is  generally  assumed  that 
the  contents  are  in  the  same  condition  as  on  leaving  the  factory. 
Probably,  however,  some  decomposition  always  takes  place  in 
transit,  as  a  smell  of  ammonia  is  often  noticed  when  the  case  is 
opened.  Convenient-sized  lumps  are  broken  off  or  picked  out 
from  as  many  different  parts  as  possible,  and  transferred  at  once 
to  a  jar  with  a  well-fitting  stopper.  These  are  crushed  to  coarse 
powder  in  a  dry,  covered  porcelain  mortar.  Great  care  must 

i  Generally  present  in  traces  only. 
455 


456  THE  CYANIDE  HANDBOOK 

be  taken  not  to  inhale  any  of  the  dust  produced  by  the  crushing. 
The  powder  is  at  once  transferred  to  a  dry  clean  jar.  As  the 
substance  is  very  hygroscopic,  and  cannot  be  heated  to  100°  C. 
without  danger  of  decomposition,  it  is  best  to  make  all  the  deter- 
minations on  the  moist  sample,  and  calculate  the  results  to  dry 
weight  after  estimating  moisture.  About  100  grams  or  less  will 
suffice  for  all  the  estimations. 

Every  portion  for  analysis  is  weighed  out  in  a  small,  accurately 
stoppered  bottle  of  known  weight.  It  is  better  to  take  roughly 
the  amount  required,  transferring  with  a  glass  spatula  to  the 
weighing  bottle.  With  a  little  practice  it  is  easy  to  take  out  the 
quantity  needed  within  about  0.1  gram.  The  exact  weight  of 
the  portion  so  taken  is  then  determined  on  an  analytical  balance 
within  0.0001  gram,  correcting  for  weight  of  bottle. 

ESTIMATION  OF  ACID  RADICALS 

Cyanogen  (as  simple  cyanides,  e.g.,  KCy,  NaCy,  CaCy2,  NH4Cy). 
—  Weigh  about  0.5  gram  of  the  sample  and  transfer  to  a  200  cc. 
conical  flask.  Dissolve  in  about  50  cc.  of  distilled  water,  rinse 
out  the  weighing  bottle  and  add  the  washings  to  the  same  flask. 
Add  5  cc.  of  neutral  1  per  cent,  potassium  iodide  solution  and 
titrate  in  the  ordinary  way  with  standard  silver  nitrate  to  the 
first  appearance  of  a  permanent  yellowish  turbidity.  (See  Section 
III.)  The  formation  of  a  granular  precipitate  near  the  finish 
generally  indicates  that  the  liquid  is  too  concentrated,  and  in 
such  cases  more  water  may  be  added.  If  the  sample  contains 
sulphides,  there  is  a  darkening  of  the  liquid  which  interferes 
with  the  silver  titration.  In  this  case  agitate  with  lead  carbon- 
ate or  preferably  a  few  drops  of  an  alkaline  lead  solution  and 
filter  before  titrating  with  AgNO3. 

Carbonates  and  Bicarbonates.  — Take  3  to  5  grams  of  the  sample, 
dissolve  in  100  cc.  distilled  water,  and  proceed  as  in  Section  III. 

Hydrates  (hydroxides).  —  It  is  generally  advisable  to  make 
a  determination  of  "protective  alkali"  by  adding  to  a  weighed 
portion  of  the  sample,  say  1  gram,  dissolved  in  water,  sufficient 
AgNO3  to  give  a  permanent  precipitate,  then  a  few  drops  of  an 
alcoholic  solution  of  phenol-phthalein,  and  titrating  with  standard 
acid.  The  result  obtained  is  the  equivalent  of  the  hydrate,  plus 
that  of  half  the  carbonate,  in  terms  of  the  standard  acid  em- 
ployed. From  this  the  amount  of  hydrate  may  be  calculated, 


ANALYSIS   OF  COMMERCIAL  CYANIDE 


457 


the  percentage  of  carbonate  being  already  known.  Bicarbonates 
cannot,  of  course,  co-exist  with  hydrates  of  the  alkali  metals, 
at  least  in  solution. 

N 
Ice.  yy;  acid  with  phenol-phthalein  indicator 

-  0.0056  gram  KOH  =  0.0138  gram  K2CO3. 
.   =  0.0040  gram  NaOH     =  0.0106  gram 


Cyanates.  —  1.  /The  writer  has  obtained  the  best  results  by 
the  method  of  O.  Herting,1  which  is  tolerably  simple  when  once 
the  necessary  apparatus  has  been  arranged.  From  3  to  5  grams 
of  the  sample  are  dissolved  in  water  in  an  evaporating  basin, 
and  sufficient  dilute  hydrochloric  acid  (say  30  to  50  cc.  of  25  per 
cent.  HC1)  are  added  to  completely  decompose  the  cyanide. 
The  mixture  is  evaporated  on  a  water-bath,  care  being  taken  to 
avoid  the  access  of  ammonia  vapors.  The  cyanide  is  decom- 


FIG  42.  — Apparatus  for  Estimation  of  Cyanates  and  Ammonium. 


posed  thus: 


NaCN  +  HC1  =  NaCl  +  HCN 


while  the  cyan  ate  gives  the  reaction 

NaCNO  +  2HC1  +  H2O  =  NaCl  +  NH4C1  +  CO2. 

The  evaporated  residue  is  then  dissolved  in  a  little  water  and 
transferred  to  a  distilling  flask,  A  (see  Fig.  42),  connected  with 
two  bulb  U-tubes,  Bt  and  B2,  or  other  similar  apparatus,  each 

N 
containing,  say,  20  cc.  of  —  acid  and  placed  in  series,  the  one 

nearest  the  distilling  flask  being  kept  cool  by  immersion.  The 
distilling  flask,  A,  is  provided  with  a  bent  inlet-tube",  a,  dipping 
under  the  surface  of  the  liquid  and  open  at  both  ends.  The 
mouth  of  the  exit  tube,  b,  is  covered  loosely  with  a  plug  of  glass 
wool,  c,  which  serves  to  prevent  the  splashing  of  any  liquid  into 

1  "Zeit.  fur  angew.  Chem.,"  XXIV,  585  (1901), 


458  THE  CYANIDE   HANDBOOK 

b  when  the  contents  of  A  are  boiled.  (Instead  of  this  contri- 
vance, the  arrangement  of  two  flasks  shown  in  Sutton's  "  Volu- 
metric Analysis/7  8th  edition,  Fig.  48,  p.  274,  may  be  used.) 
The  apparatus  is  also  connected  with  an  aspirator,  D,  or  other 
means  by  which  a  slow  current  of  air  may  be  drawn  through 
uninterruptedly  for  about  thirty  minutes.  The  wash-bottle, 
Cj  contains  dilute  acid  and  is  connected  with  the  tube  a  by  a 
joint  at  e  at  a  later  stage. 

When  everything  is  ready,  the  current  of  air  is  started  by 
opening  the  clip  at  /.  About  10  cc.  of  normal  NaOH  are  intro- 
duced by  holding  a  vessel  containing  the  alkali  under  the  open 
end  of  tube  a.  The  flask  C  is  then  connected  with  a  and  serves 
to  prevent  the  introduction  of  any  ammonia  vapor  from  the  air 
of  the  laboratory.  The  liquid  in  A  is  boiled  very  gently  for  fifteen 
minutes,  avoiding  violent  ebullition  or  too  great  concentra- 
tion. The  lamp  is  then  removed  and  the  air  current  continued 
for  some  time  longer.  The  apparatus  is  then  detached  at  d 
and  the  contents  of  the  bulb  tubes,  Bl  and  52,  together  with  any 

N 
liquid  condensed  in  6,  are  collected  and  titrated  with  • —  sodium 

N 
hydrate  and  methyl  orange  indicator.     The  amount  of  —  acid 

taken,  less  that  found  in  the  final  titration,  indicates  the  amount 
of  ammonia  evolved,  and  hence,  by  calculation,  the  amount  of 
cyanate. 

When  the  sample  originally  also  contained  ammonium  salts, 
the  ammonium  must  be  separately  determined  (see  Section  III) 
and  the  amount  found  deducted  from  the  total  ammonium  given 
by  the  test  just  described.  The  difference  is  then  calculated  to 
cyanate. 

2.  An  extremely  simple  method  of  estimating  cyanates  has 
been  described  by  A.  C.  Gumming  and  O.  Masson,1  which,  if 
reliable,  would  seem  to  be  the  best  method  so  far  announced. 
A  known  volume  of  the  solution  is  first  titrated  for  "total  alkali," 
as  described  in  Section  III,  using  methyl  orange  or  Congo  red 
as  indicator.  A  measured  excess  of  the  acid  is  then  added.  The 
mixture  is  then  boiled  for  a  few  minutes,  when  the  decomposition 
given  in  the  previous  method  takes  place,  and  CO2  is  driven  off. 

1  "Proc.  Soc.  Chem.  Ind.  of  Victoria,"  July-August,  1903.  See  also  "Chenu 
News,"  Jan.  5,  1906. 


ANALYSIS   OF  COMMERCIAL  CYANIDE  459 

The  solution  is  cooled  and  more  of  the  indicator  added  if  necessary. 
The  residual  acid  is  then  titrated  with  standard  alkali. 

Ice.  j^  acid  consumed  =  0.003253  gram  NaCNO. 

Of  course,  only  that  portion  of  acid  is  considered  which  is 
added  after  the  neutralization  of  total  alkali  in  the  cold.  The 
analyses  reported  by  the  authors  are  satisfactory. 

Chlorides.  —  See  Section  III. 

Ferrocyanides.  —  Any  soluble  iron  will  pretty  certainly  be 
present  as  ferrocyanide.  As  the  amount  is  commonly  very 
small,  a  large  amount,  say  10  grams,  of  the  cyanide  is  dissolved 
and  filtered.  The  filtrate  is  decomposed  (under  a  hood)  with 
HC1,  and  finally  with  H2SO4,  the  iron  precipitated  with  ammonia 
and  determined  by  the  colorimetric  test.  (See  Section  I.) 

Silicates.  —  Five  grams  of  the  sample  are  evaporated  to  dry- 
ness  with  excess  of  HC1,  ignited  gently  to  render  silica  insoluble, 
taken  up  with  HC1  and  hot  water,  boiled  and  filtered,  and  washed 
free  from  chlorides.  The  residue  is  ignited  and  weighed  as  Si02. 

Sulphides.  —  In  the  brands  of  cyanide  commonly  manufac- 
tured at  the  present  day,  the  amount  of  soluble  sulphide  is  very 
small.  It  may  be  estimated  by  the  method  of  C.  J.  Ellis.  (Section 
III.)  When  in  larger  quantities,  precipitate  a  solution  of  say 
10  grams  of  the  sample  with  alkaline  lead  tartrate;  filter,  wash 
free  from  cyanide,  burn  the  paper  in  a  weighed  crucible,  add 
HNO3  and  H2SO4.  Evaporate  cautiously  to  dry  ness,  ignite 
gently,  and  weigh  as  PbS04. 

Sulphates  and  Thiocyanates.  —  See  Section  III. 

Thio sulphates,  if  present  in  any  considerable  quantity,  may 
lead  to  serious  errors  in  the  estimation  of  cyanide,  owing  to  the 
solubility  of  AgCy  in  alkaline  thiosulphates.  They  may  generally 
be  detected  by  the  formation  of  a  white  precipitate  on  addition 
of  a  mineral  acid;  tartaric  acid  gives  no  precipitate.  For  esti- 
mation see  Section  III.1 

ESTIMATION  OF  METALLIC  RADICALS 

Sodium.  —  This  is  usually  the  principal  metal  in  cyanide 
samples,  and  is  separated  together  with  potassium.  A  preliin- 

»See  also  W.  Fold,  "Journ.  fur  Gasbeleuchtung,"  XL VI,  561;  "Journ.  So<j. 
Chem.  Ind.,"  Sept.  30,  1903, 


460  THE  CYANIDE  HANDBOOK 

inary  qualitative  test  is  desirable,  to  determine  whether  iron, 
calcium,  or  other  metals  are  present  in  appreciable  quantities. 
About  1  gram  or  more  of  the  sample  is  dissolved  in  water  in  a 
weighed  porcelain  (or,  better,  platinum)  dish,  excess  of  HC1  added 
and  evaporated  to  dryness,  finishing  on  a  water-bath  and  finally 
heating  very  cautiously,  to  avoid  decrepitation,  till  the  ammo- 
nium salts  are  expelled.  Moisten  with  a  few  drops  of  HC1  and 
again  evaporate  to  complete  dryness. 

1.  In  the  absence  of  appreciable  amounts  of  metals  other 
than  Na  and  K,  or  of  insoluble  matter  (SiO2,  etc.),  it  is  sufficient  to 
weigh  the  dish  and  contents,  after  cooling  in  a  desiccator,  and  to 
dissolve  the  residue  in  water  and  make  up  to  a  definite  volume. 
Take  out  an  aliquot  part  of  this  solution,   and  determine  the 
chlorine  by  titration  with  silver  nitrate  and  chromate  indicator. 
Examine  another  portion  of  the  solution  for  sulphates;  if  found, 
determine  by  heating  to   boiling,   acidifying  slightly  with  HC1 
and  precipitating  with  BaCl2.     Deduct  the  equivalent  of  the  total 
01  and  SO4  present  from  the  total  weight  of  the  ignited  residue. 
The  difference  gives  xNa  +  yK. 

Where  only  chlorides  are  found,  the  quantities  of  sodium  and 
potassium  may  be  calculated  from  the  formula  given  in  Section 
I  (under  "Potassium").  This  method  is,  however,  not  reliable 
when,  as  is  usually  the  case  in  cyanide  samples,  one  of  the  alkali 
metals  is  largely  in  excess  of  the  other. 

2.  In  cases  where  silica,  iron,  etc.,  are  present,  the  sample 
is  first  evaporated  with  HC1,  then  re-dissolved  in  a  little  hot 
dilute   HC1,   precipitated   with   ammonia,    and   filtered.    ,If  the 
precipitate  is  considerable,  it  is  re-dissolved  and  re-precipitated. 
Metals  other  than  Fe,  Al,  Ca,  and  Mg  are  rarely  present  in  per- 
ceptible quantities,  so  that  it  is  generally  sufficient  to  employ 
the  ordinary  methods  of  separation  with  ammonium  oxalate  and 
carbonate.    (See  Section  I.)    No  special  precautions  need  be  taken 
to  remove  sulphates,  as  it  is  more  convenient  to  determine  the 
SO4  remaining  at  the  end  of  the  operation  in  the  final  solution, 
as   already   described.     Finally   evaporate   and   ignite   to   expel 
ammonium  salts,  again  moisten  with  HC1,  dry,  ignite,  cool  in 
desiccator,  and  weigh  dish  and  contents. 

Potassium.  —  It  will  generally  be  necessary  to  make  a  sep- 
arate determination  of  this  metal  whenever  a  complete  analysis 
is  required.  When  the  potassium  is  largely  in  excess  of  the  so- 


ANALYSIS   OF  COMMERCIAL  CYANIDE  461 

dium,  it  is  perhaps  best  determined  by  Tatlock's  method  *  (see 
Section  I),  p.  421.  In  cases  where  the  sodium  largely  exceeds  the 
potassium,  as  in  samples  of  the  sodium  cyanide  in  ordinary  use 
in  cyanide  treatment,  Finkener's  method  is  preferable  (see  Sec- 
tion I,  method  No.  3),  p.  422. 

Ammonium.  —  Dissolve  3  to  5  grams  of  the  sample,  precip- 
itate completely  with  AgNO3;  'i.e.,  add  sufficient  to  convert  all 
cyanides  into  AgCy,  and  thiocyanates,  ferrocyanides,  and  cyan- 
ates  into  silver  salts,  leaving  a  small  excess  of  AgN03  in  the  solu- 
tion. Filter,  add  a  few  drops  of  HC1  or  NaCl  to  remove  excess  of 
silver,  concentrate  to  a  moderate  bulk,  filter  into  a  distilling 
flask,  and  distil  with  NaOH  as  described  under  "Cyanates" 
(see  above),  collecting  the  distillate  in  standard  acid.  Titrate 
residual  acid  with  standard  alkali. 

N 
Ice.  ^  acid  consumed  =  0.0018042  gram  NH4. 

Other  metals  are  determined  by  the  ordinary  methods  of 
analysis  after  decomposing  the  cyanide. 

MOISTURE  AND  INSOLUBLE  MATTER 

Moisture.  —  About  5  grams  of  the  sample  are  weighed  in  a 
rather  large  weighing  bottle  and  the  open  bottle  placed  in  a 
desiccator  over  strong  sulphuric  acid  for  at  least  three  hours, 
and  weighed  after  replacing  the  stopper.  The  bottle  is  then 
left,  unstopperedr  in  the  desiccator  for  another  hour  and  again 
weighed.  The  weighings  are  repeated  at  intervals  of  an  hour 
until  the  loss  of  weight  becomes  negligible.  It  is  advisable  to 
have  some  absorbent  of  carbonic  acid  also  present  in  the  desic- 
cator, as  a  slight  but  measurable  decomposition  of  cyanide  may 
otherwise  take  place,  due  to  atmospheric  carbonic  acid.  A 
slight  loss  of  cyanogen  also  generally  occurs  on  drying  at  100°  C., 
even  in  an  atmosphere  free  from  carbonic  acid.  Ammonium 
cyanide,  if  originally  present  in  the  sample,  is  volatilized  at  a 
temperature  far  below  100°  C. 

Insoluble  matter.  —  If  any  portion  of  the  sample  is  insoluble 
in  water,  it  is  advisable  to  weigh  out  at  least  10  grams,  dissolve 
to  a  liter,  collect  on  a  weighed  filter,  and  wash  with  warm  water 
till  free  from  cyanide.  This  residue  may  consist  of  silica,  ferric 

»  For  details  see  A.  H.  Low,  "Technical  Methods  of  Ore  Analysis,"  p.  1$4. 


462  THE  CYANIDE  HANDBOOK 

oxide,  free  carbon,  carbide  of  iron,  etc.  After  drying  at  100°  C., 
it  is  weighed  with  the  paper,  then  ignited  and  again  weighed, 
deducting  ash  of  paper.  The  amounts  of  volatile  and  non- 
volatile constituents  in  the  insoluble  matter  are  thus  ascer- 
tained. 

CALCULATION  OF  RESULTS 

This  is  generally  done  by  an  arbitrary  rule  as  follows:  The 
whole  of  the  K  and  NH4  are  calculated  as  cyanides.  NH4  may 
exist  in  other  forms,  as  NH4C1,  etc.,  but  these  are  probably 
completely  converted  into  NH4Cy  on  dissolving  in  water  in  pres- 
ence of  a  large  excess  of  KCy  or  NaCy.  The  remaining  Cy  is 
calculated  as  NaCy.  Any  Na  in  excess  is  distributed  among  the 
other  acid  radicals  to  form  carbonates,  cyanates,  chlorides,  etc., 
according  to  the  amounts  of  these  found  in  the  analysis.  Iron 
in  soluble  form  is  calculated  to  ferrocyanide. 


SECTION   V 

ANALYSIS  OF  SUNDRY  MATERIALS  USED  IN  CONNEC- 
TION  WITH   THE   CYANIDE   PROCESS 

A.    LIME 

LIME  is  universally  used  as  a  neutralizing  agent,  and  is  fre- 
quently added  in  the  battery  to  counteract  the  effect  of  soluble 
acid  salts  in  the  mill  or  mine  water;  it  is  also  used  as  a  coagula- 
ting agent  in  bringing  about  the  settlement  of  slimes.  It  is  added 
to  the  cyanide  solution  as  a  protection  against  soluble  and  insol- 
uble cyanicides  in  the  material  treated,  and  also  against  atmos- 
pheric carbonic  acid.  For  the  former  purpose  carbonate  of 
lime  may  be  used,  100  parts  of  CaCO3  being  equivalent  to  56 
parts  of  CaO.  For  direct  use  in  conjunction  with  cyanide  solu- 
tion, however,  only  the  soluble  CaO  or  Ca(OH)2  is  of  any  prac- 
tical value.  Under  certain  circumstances,  therefore,  separate 
determinations  of  the  total  Ca,  and  of  the  equivalent  of  alkali 
present  as  CaO  or  Ca(OH)2,  become  necessary. 

E.  H.  Croghan  1  notes  the  following  substances  as  occurring 
in  " burnt  lime"  supplied  in  the  Transvaal  for  use  in  cyanide 
plants:  Lime  (CaO)  total,  as  oxide  and  hydrate;  Magnesia  (MgO); 
Ferric  oxide  (Fe203);  Alumina  (A1203),  probably  as  aluininates; 
Manganese  dioxide  (MnO2);  Carbon  dioxide  (CO2),  in  combination 
as  carbonates;  Quartz  and  insoluble  matter;  Soluble  silica  (as 
compound  silicates);  sulphuric  acid  (SO3),  in  calcium  sulphate; 
Phosphoric  acid  (P2O5)  —  traces  only;  Moisture,  water  of  hydra- 
tion,  in  Ca(OH)2,  etc;  Carbon,  from  decomposition  of  organic 
matter.  In  the  unburnt  limestone  the  iron  and  manganese  are 
probably  present  as  ferrous  and  manganous  carbonates  (FeCO3 
and  MnCO3). 

Sampling  and  Preparation.  —  Quicklime  exposed  to  the  air 

i  E.  H.  Croghan.      "Journ.  Chem.  Met.  and  Min.  Soc.  of  S.Africa,"  VIII  (2) 
August,  1907,  pp.  37-41. 

463 


464  THE  CYANIDE  HANDBOOK 

gradually  absorbs  moisture  and  carbonic  acid;  in  sampling  and 
in  preparing  the  sample  for  analysis,  care  must  therefore  be  taken 
to  exclude  air  and  moisture  as  much  as  possible.  The  sample 
is  crushed  as  quickly  as  possible  till  fine  enough  to  pass  a  60-mesh 
sieve,  and  preserved  in  stoppered  bottles. 

Estimation  of  Constituents  other  than  Caustic  Lime.  —  The  vari- 
ous metals  and  acid  radicals  contained  in  samples  of  ordinary 
quick-  or  slaked-lime  can  all  be  estimated  by  the  methods  already 
described.  (See  above.)  The  portion  for  analysis,  in  which  the 
metals  are  to  be  determined,  is  dissolved  in  hydrochloric  acid, 
evaporated  to  dryness  on  the  water-bath,  taken  up  with  dilute 
HC1,  filtered,  and  the  filtrate  again  evaporated  on  the  water- 
bath  to  render  silica  insoluble.  A  separate  determination  should 
be  made  of  soluble  and  insoluble  silica,  and  of  carbonic  acid.  (See 
Section  I.) 

Estimation  of  Caustic  Lime.  — •  Caustic  lime  may  be  taken  to 
mean  the  equivalent  in  terms  of  CaO  of  the  whole  of  the  calcium 
existing  as  calcium  oxide  (CaO)  and  as  calcium  hydroxide  Ca(OH)2. 
There  are  three  methods  in  general  use  for  this  determination. 

1.  The  total  calcium  is  determined,  and  the  amounts  present 
as  carbonate,  sulphate,  aluminate,  phosphate,  etc.,  are  deducted. 
The  remainder  is  calculated  as  CaO. 

2.  A   small  weighed  portion   of  the   sample  is   mixed  with 
water,  heated  to  boiling,  and  titrated  with  standard  acid  and 
phenol-phthalein.1 

3.  The  portion  for  analysis  is  agitated  with   a  solution  of 
sugar  in  water,  allowed  to  stand  for  a  considerable  time,  again 
agitated  and  allowed  to  settle,  and  an  aliquot  part  of  the  solu- 
tion titrated  with  standard  acid  and  phenol-phthalein.2 

The  first  method  is  somewhat  complicated,  and  liable  to  seri- 
ous error,  owing  to  the  difficulty  of  determining  exactly  in  what 
forms  the  calcium  exists  in  commercial  lime.  The  second  method, 
according  to  Croghan  (loc.  cit,  p.  39),  appears  to  yield  satisfactory 
results  in  the  case  of  lime  containing  little  or  no  magnesia,  but 
gives  entirely  erroneous  results  with  lime  containing  24  per 
cent,  or  more  of  MgO,  or  with  the  so-called  "blue  lime,"  which 
also  contains  considerable  amounts  of  MnO2.  It  would  not  be 
permissible  to  reckon  the  magnesia  (MgO)  as  "caustic  lime" 

1  Sutton,  "Volumetric  Analysis,"  8th  edition,  p.  76. 

2G.  W.  Williams,  "Proc.  Chem*.,  Met.  and  Min.  Soc.  of  S.  A.,"  April,  1905. 


ANALYSIS   OF  SUNDRY  MATERIALS  465 

for  our  present  purpose,  as  it  is  practically  insoluble  in  cold 
water.  The  third  or  "  sugar  "  method  seems  to  be,  on  the  whole, 
the  best  so  far  suggested.  It  is  carried  out  as  follows:  2  grams 
of  the  sample  are  transferred  to  a  liter  flask,  which  is  then  filled 
up  to  the  mark  with  a  solution  containing  20  grams  pure  cane 
sugar  per  liter.  The  mixture  is  thoroughly  shaken  at  intervals 
for  an  hour,  allowed  to  stand  over  night,  again  shaken  for  a 
minute  or  two,  allowed  to  settle,  and  an  aliquot  part,  say  250  cc., 
taken  out  and  titrated  with  normal  HC1,  using  phenol-phthalein 
as  indicator.  When  methyl  orange  is  used  as  indicator,  too  high 
a  result  is  obtained,  as  the  lime  present  as  aluminate,  alumino- 
silicate,  and  perhaps  some  other  forms,  is  also  indicated.  These 
compounds  appear  to  be  soluble  in  the  sugar  solution,  but  not 
so  to  any  large  extent  in  pure  water. 

Practically  identical  results  were  obtained  by  Croghan  in 
some  cases  by  using  ordinary  distilled  water  instead  of  sugar- 
water,  and  titrating  as  above  with  normal  acid  and  phenol- 
phthalein,  but  as  lime  is  more  soluble  in  the  sugar-water,  the 
result  is  obtained  more  quickly  by  that  method. 

B.   COAL 

The  determinations  commonly  required  for  estimating  the 
value  of  coal  are:  moisture,  volatile  matter,  fixed  carbon,  ash, 
calorific  power.  Occasionally,  sulphur,  phosphorus,  iron,  or 
other  constituents  have  to  be  determined. 

Preparation.  —  The  sample  is  crushed  and  quartered  as  in 
the  case  of  ores.  A  portion  of  the  coarsely  crushed  sample  is 
reserved  for  the  moisture  determination.  As  the  finely  crushed 
coal  loses  or  absorbs  moisture  and  is  liable  to  undergo  other 
changes  on  exposure,  the  sample  must  be  kept  in  a  well-stoppered 
bottle. 

Moisture.  —  One  gram  or  more  of  the  coarsely  crushed  coal 
is  dried  for  an  hour,  at  about  105°  C.,  in  an  open  crucible,  which 
is  then  cooled  in  a  dessiccator,  covered,  and  weighed.  Another 
determination  of  moisture  is  made  on  the  finely  ground  portion, 
for  the  purpose  of  correcting  the  determinations  of  volatile 
matter,  carbon,  and  ash  which  are  made  on  the  fine  sample. 

Volatile  Matter  (other  than  moisture) .  —  One  gram  of  the 
finely  powdered  sample  is  heated  in  a  large,  tightly  covered  plat- 
inum crucible  over  a  gas  flame  for  seven  minutes,  gently  at  first, 


466  THE  CYANIDE  HANDBOOK 

finally  with  the  full  flame  of  the  burner.  When  no  more  flame 
is  seen  over  the  cover,  cool  and  weigh.  This  is  an  entirely  arbi- 
trary test,  as  by  heating  at  a  higher  temperature  more  volatile 
matter  is  expelled,  but  it  serves  as  a  ready  means  of  comparing 
the  quality  of  different  samples  of  coal. 

Fixed  Carbon.  —  This  is  generally  found  by  difference  after 
determining  volatile  matter,  ash,  and  moisture.  There  is  an 
error  in  this,  as  in  many  cases  a  part  of  the  sulphur  is  not  in- 
cluded either  in  volatile  matter  or  ash. 

Ash.  —  This  may  be  determined  either  by  strongly  igniting, 
in  an  open  vessel,  the  coke  left  after  determining  volatile  matter, 
or  (better)  by  igniting  a  fresh  quantity  of  the  original  finely 
powdered  sample  in  an  open  crucible  till  all  combustible  matter 
is  burnt  off.  It  is  necessary  to  heat  gently  at  first  and  gradually 
raise  the  temperature. 

Calorific  Power.  —  This  is  a  determination  of  the  heat  given 
off  in  the  complete  combustion  of  a  given  weight  of  the  coal.  It 
is  carried  out  by  instruments  known  as  "  calorimeters,"  the  gen- 
eral principle  being  that  the  combustion  takes  place  inside  a 
closed  vessel  surrounded  by  water,  the  heat  of  combustion  being 
calculated  from  the  rise  of  temperature  of  the  water,  with  correc- 
tions, depending  on  the  particular  instrument,  for  losses  of  heat 
by  radiation  and  in  heating  the  vessel  itself.  The  powdered 
coal,  mixed  with  some  powerful  oxidizer,  such  as  potassium 
nitrate  or  chlorate,  is  placed  in  a  copper  cylinder  or  other  suitable 
receiver,  ignited,  and  quickly  placed  in  the  larger  vessel  filled 
with  water  of  known  mass  and  temperature.  When  the  action 
is  complete,  the  water  is  agitated  and  the  temperature  of  the 
water  again  taken. 

The  calorific  power  of  the  coal  is  expresed  in  thermal  units, 
each  of  which  is  equal  to  the  quantity  of  heat  required  to  raise 
unit  mass  of  water  at  its  maximum  density  through  one  degree 
of  temperature.  The  British  unit  is  the  heat  required  to  raise 
1  Ib.  av.  of  water  from  39.1°  to  40.1°  F. 

The  Calorie  (metric  unit)  is  the  heat  required  to  raise  1  kg. 
from  4°  to  5°  C. 

Sulphur  is  generally  determined  by  Eschka's  method,1  which 
has  been  adopted  as  a  standard.  An  intimate  mixture  of  the 

1  For  details  see  A.  H.  Low,  "Technical  Methods  of  Ore  Analysis,"  3d  edition, 
p.  272. 


ANALYSIS   OF  SUNDRY  MATERIALS  467 

finely  powdered  coal  with  magnesia  and  sodium  carbonate  is 
gradually  heated  to  dull  redness,  stirring  till  carbon  is  burnt 
off.  The  residue  is  treated  with  bromine  water,  filtered,  and  the 
filtrate  boiled  with  HC1  to  expel  excess  of  bromine.  It  is  then 
precipitated  with  barium  chloride  and  the  sulphur  estimated  in 
the  usual  way  as  BaSO4. 

Phosphorus.1  —  This  is  determined  in  the  ash  from  (say) 
5  grams  of  the  sample.  The  ash  is  digested  with  HC1,  filtered, 
washed,  and  the  filtrate  evaporated  to  dryness.  It  is  then  treated 
with  strong  HNO3,  filtered  and  diluted,  then  precipitated  with 
ammonic  nitromolybdate  at  40°  to  45°  C.  After  agitating  thor- 
oughly and  allowing  to  settle,  the  precipitate  is  collected  on  a 
weighed  filter,  washed  with  2  per  cent,  nitric  acid,  till  free  from 
soluble  matter,  and  finally  with  alcohol.  It  is  then  dried  for 
twenty  minutes  at  110°  C.  and  weighed  as  ammonium  phospho- 
molybdate.  (See  Section  I.) 

Iron.  —  This  may  also  be  determined  in  the  ash  from  1  to  5 
grams  of  the  finely  powdered  coal.  Evaporate  to  dryness  with 
HC1,  filter,  add  a  little  HNO3,  dilute,  heat  to  boiling,  and  precip- 
itate with  ammonia.  Wash,  re-dissolve  in  dilute  H2SO4,  reduce 
to  the  ferrous  state,  and  titrate  with  permanganate.  (See  Sec- 
tion I.) 

C.   WATER 

The  quality  of  the  water  used  in  a  cyanide  plant  for  various 
purposes,  such  as  for  boilers,  for  making  up  solutions,  etc.,  is 
often  a  matter  o£  very  great  importance.  Water  which  is  very 
acid  or  highly  charged  with  mineral  salts  should  be  avoided 
whenever  possible,  as  also  water  containing  large  amounts  of 
dissolved  organic  matter.  On  the  other  hand,  the  water  may 
contain  much  common  salt  without  being  rendered  unfit  for 
making  up  working  solutions.  Very  salt  water  is  used  in  some 
plants  in  Western  Australia.  In  general  there  is  no  necessity 
for  a  complete  analysis.  For  example,  a  rough  test  will  suffice 
for  determining  the  total  amount  of  organic  matter.  The  follow- 
ing are  the  more  important  determinations:  Acidity  or  alkalinity; 
Total  dissolved  solids;  Solids  in  suspension;  Hardness;  Metallic 
radicals  (calcium,  magnesium,  sodium,  and  potassium:  others 
are  less  important) ;  Non-metallic  radicals  (carbonates,  sulphates, 
chlorides:  others  are  less  important). 

1  ibid.,  p.  274. 


468  THE  CYANIDE  HANDBOOK 

Sampling.  —  Use  a  large,  clean,  stoppered  bottle.  Rinse 
well  with  the  water  to  be  sampled;  if  possible,  immerse  the  bottle. 
Avoid  surface  water  and  deposits  at  the  bottom.  If  sampling 
from  a  pump  or  tap,  allow  some  water  to  run  to  waste  before 
collecting  sample,  so  as  to  avoid  taking  water  which  has  been 
standing  in  the  pipe.  Fill  the  bottle  completely  and  empty 
again  so  as  to  expel  any  gases  which  might  have  been  in  the 
bottle;  then  fill  again  nearly  to  the  stopper.  Keep  stoppered 
when  not  in  use. 

Preliminary  Observations.  —  Note  color,  taste,  and  smell; 
particularly  observe  whether  there  is  much  suspended  matter. 
Measure  or  weigh  the  whole  sample.  Allow  to  settle.  If  pos- 
sible, decant  as  much  as  can  be  drawn  off  clear,  measure  this 
and  keep  separate.  Filter  the  remainder  through  a  weighed 
filter-paper  dried  at  100°  C.  For  very  accurate  work  the  filter- 
papers  are  previously  washed  with  HC1  until  all  iron,  etc.,  is 
removed,  then  washed  thoroughly  with  distilled  water,  and  dried 
at  100°  C.  before  use. 

Alkalinity  or  Acidity.  —  To  100  cc.  of  the  filtered  water  add 
one  or  two  drops  of  a  0.5  per  cent,  alcoholic  solution  of  phenol- 
phthalein.  If  a  pink  color  appears,  alkaline  hydrates  or  mono- 
carbonates  are  probably  indicated,  though  in  some  cases  the 
reaction  might  be  due  to  sulphides,  cyanides,  or  other  alkaline 

N 


salts,  or  to  free  ammonia.     Titrate  with  very  dilute  f  say  j 

\         100/ 

acid  until  the  color  just  disappears. 

To  another  100  cc.  of  the  filtered  water  add  one  or  two  drops 
of  a  0.1  per  cent,  aqueous  solution  of  methyl  orange.  A  pink 

N 

color  indicates  acidity.     In  this  case,  titrate  with  alkali  till 

100 

the  color  just  disappears.     If  no  pink  color  is  given  by  methyl 

N 

orange,  titrate  with acid  until  the  tint  just  appears. 

luu 

It  frequently  happens  that  the  same  water  may  appear  neu- 
tral or  even  acid  to  phenol-phthalein  and  alkaline  to  methyl 
orange.  This  is  owing  to  the  presence  of  bicarbonates  or  of  free 
carbonic  acid.  Phenol-phthalein  is  affected  by  monocarbonates 
of  the  alkali  metals,  but  not  by  bicarbonates,  and  is  also  sensi- 
tive to  carbonic  acid,  whereas  methyl  orange  is  affected  by  both 
mono-  and  bicarbonates,  which  act  as  alkalis  towards  it,  while 


ANALYSIS   OF  SUNDRY  MATERIALS  469 

it  is  not  sensitive  to  carbonic  acid.1  The  following  possible 
conditions  are  to  be  considered :  (a)  The  water  may  contain  bicar- 
bonates  and  free  carbonic  acid,  (b)  The  water  may  contain  car- 
bonates and  bicarbonates.  (c)  The  water  may  contain  hydrates 
and  carbonates,  (d)  Carbonates  alone  may  be  present,  (e) 
Bicarbonates  alone  may  be  present. 

(a)   Bicarbonates  and  Free  Carbonic  Acid.  —  The  water  is  acid 
to  phenol-phthalein  and  alkaline  to  methyl  orange. 

W 

(i)  To  one  portion  add  phenol-phthalein  and  run  in alkali 

1UU 

gradually,  without  violent  agitation,  till  the  pink  color  just 
appears.  This  indicates  free  CO2,  the  reaction  being  NaOH  + 
CO2  =  NaHCO3,  or  its  equivalent. 

Ice.  ^  alkali  =  0.00044  gram  CO2. 

(ii)  To  another  portion  add  methyl  orange  and  titrate  with 
acid  till  a  pink  tint  is  just  produced. 


100 

NaHCO3  +  HC1  =  NaCl  +  H2O  +  CO2. 
Ice.  —  acid       =  0.00044  gram  CO2  as  bicarbonate. 
=  0.00084  gram  NaHCO3. 

(iii)  To  confirm  this  last  result,  take  another  portion  of  the 
water,  boil  for  five  minutes,  cool  and  add  phenol-phthalein.  The 
water  will  now  be  alkaline  to  this  indicator;  free  CO2  has  been 
expelled  and  bicarbonates  decomposed  thus: 

2NaHC03  -  Na2C03  +  H2O  +  CO2. 

N 

Titrate  with acid: 

JLUU 

Na2CO3  +  HC1  =  NaHCO3  +  NaCl. 

N 
Ice.  YQQ  acid      =  0.00088  gram  CO2  originally  as  bicarbonate. 

=  0.00168  gram  NaHCO3. 

(b)  Carbonates  and  Bicarbonates.  —  The  water  is  alkaline  to 
both  indicators. 

N 

(i)  Titrate  with  —  acid  and  phenol-phthalein. 
100 

i  See  Sutton,  "Volumetric  Analysis,"  8th  edition,  p.  105. 


470  THE  CYANIDE  HANDBOOK 

Reaction: 

Na2C03  +  HC1  -  NaHCOs  +  NaCl. 
N 
Ice.  Y^T  acid  =  0.00044  gram  CO2  as  carbonate. 

=  0.00106  gram  Na2CO3. 

N 

(ii)  Titrate  with acid  and  methyl  orange. 

100 

Reactions : 

Na2CO3  +  2HC1  =  2  NaCl  +  H2O  +  CO2 
NaHCO3  +    HC1  =  NaCl  +  H2O  +  CO2.    ' 
Let  <£  =  no.  of  cc.  required  with  phenol-phthalein ; 

ju,    =  no.  of  cc.  required  with  methyl  orange, 
using  the  same  volume  of  water  for  the  test  in  each  case. 
Then 

(f>  X  0.00044  =  gram  CO2  as  carbonate; 
(/A  -  20)  X  0.00044  =  gram  CO2  as  bicarbonate. 

(c)  Hydrates  and  Carbonates.  —  The  water  is  alkaline  to  both 
indicators. 

N 

(i)  Titrate  with  — —  acid  and  phenol-phthalein. 
100 

Reactions: 

NaOH  +  HC1  =  NaCl  +  H2O. 
Na2CO3  +  HC1  =  NaHCOa  +  NaCl. 

Ice.  ^  acid  =  0.0004    gram  NaOH. 

J-LfU 

=  0.00044  gram  CO2  as  carbonate. 

N 

(ii)  Titrate  with  — •  acid  and  methyl  orange. 
100 

Reaction : 

NaOH  +    HC1  =  NaCl  +  H2O. 

Na2CO3  +  2HC1  =  2NaCl  +  H2O  +CO2. 
(2</>  -  /A)  X  0.0004  =  grams  hydrate,  as  NaOH. 
(  /A  -  0)  X  0.00044  =  grams  CO2  as  carbonate. 

(d)  Carbonates  Alone  Present.  —  The  water  is  alkaline  to  both 
indicators,  ^  =  2  <f>. 

<t>  X  0.00044  =  grams  CO2  as  carbonate. 
A*  X  Q.00022  =  grams  CO2  as  carbonate. 

(e)  Bicarbonates  Alone  Present.  —  The   water   is   neutral  to 
phenol-phthalein  and  alkaline  to  methyl  orange. 

At  X  0.00044  =  grams  CO2  as  bicarbonate. 


ANALYSIS   OF  SUNDRY  MATERIALS  471 

These  formulae  are  not  applicable  where  other  alkalis,  such  as 
ammonia,  sulphides,  or  cyanides,  are  present  in  the  water.  The 
carbonates  occurring  in  ordinary  waters  are  those  of  the  alkali 
metals  (Na  and  K),  and  also  those  of  the  metals  Ca,  Mg,  Fe, 
Mn,  held  in  solution  by  the  excess  of  carbonic  acid,  and  perhaps 
forming  unstable  compounds  analogous  to  the  alkaline  bicar- 
bonates. 

•  Carbonic  Acid.  —  The  following  method  for  determining  total 
carbonic  acid  (free  and  combined)  may  be  used  as  a  check  on 
the  titration  given  above.  A  measured  volume  (100  to  200  cc.) 
of  the  water  is  mixed  with  a  slight  excess  of  ammonia  and  suffi- 
cient calcium  chloride  solution  to  precipitate  all  the  C02  present 
as  CaCO3.  The  flask  is  immersed  for  two  hours  in  a  vessel  of 
boiling  water.  The  precipitate  is  washed  by  decantation  with 
hot  water  containing  a  little  ammonia.  The  liquid  poured  off 
is  filtered,  and  the  washing  continued  till  the  residue  is  free  from 
chlorides.  Any  material  collected  on  the  filter  is  then  washed 
back  into  the  flask,  standard  acid  is  added  in  excess,  and  the 

N 

residual  acid  titrated  with alkali  and  methyl  orange. 

100 

CaCO3  +  2HC1  =  CaCl2  +  CO2  +  H2O. 
Ice.  ^  acid  =  0.00022  gram  CO2. 

Solids  in  Suspension  and  Solution.  —  These  are  determined  as 
described  in  Section  III  (for  cyanide  solutions),  except  that  the 
solids  in  solution  may  generally  be  evaporated  at  a  higher  tem- 
perature, first  on  a  water-bath  and  finally  in  an  air-bath  at  150° 
C.  Care  must  be  taken  not  to  heat  sufficiently  to  expel  CO2 
from  carbonates  or  to  decompose  and  char  any  organic  matter. 
After  cooling  and  weighing  it  is  sometimes  desirable  to  determine 
the  weight  of  residue  on  ignition  at  a  low  temperature.  The 
/  dish  is  heated  until  organic  matter  is  burnt  off,  without  however, 
decomposing  carbonates.  The  remaining  residue  may  be  used 
for  determination  of  SiO2,  Fe203,  A12O3,  CaO,  MgO,  etc. 

Hardness.  —  The  "  hardness "  of  water  is  estimated  by  the 
amount  of  calcium  carbonate  contained.  One  degree  of  hard- 
ness =  1  grain  CaCO3  per  gallon.  It  may,  therefore,  be  calcu- 
lated from  the  amount  of  calcium  carbonate  found  in  the 
analysis.  For  Clark's  test  with  soap  solution,  see  Sutton,  "  Volu- 


472  THE  CYANIDE   HANDBOOK 

metric  Analysis,"  8th  edition,  p.  488.  "  Permanent  hardness " 
is  generally  measured  by  the  amounts  of  calcium  and  magnesium 
sulphates  present. 

Sulphates.  —  Except  in  the  case  of  water  containing  consider- 
able quantities  of  organic  matter,  silicates  or  nitrates,  the  sul- 
phuric acid  may  be  estimated  directly  by  acidulating  a  measured 
volume  with  HC1,  heating  to  boiling,  and  precipitating  with 
BaCl2  in  the  usual  way.  Where  interfering  substances  are  pres- 
ent, evaporate  to  dryness  with  HC1,  ignite  and  re-dissolve  residue 
in  dilute  HC1  before  precipitating  with  BaCl2. 

Chlorides.  —  If  the  water  is  approximately  neutral  these 
may  be  estimated  by  titration  with  standard  AgNO3  and  neutral 
chromate  indicator.  If  acid  or  alkaline,  neutralize  with  standard 
NaOH  or  HNO3  as  required  before  adding  AgNO3.  If  there  be 
any  doubt  as  to  the  end-point,  pour  off  half  the  liquid  into  an- 
other vessel,  add  another  drop  of  AgNO3  to  one  portion,  and 
compare  the  tints;  if  any  difference  is  observed  the  titration  may 
be  regarded  as  having  been  finished  before  adding  the  extra  drop.1 
When  the  water  is  strongly  alkaline,  it  is  perhaps  better  to  add 
excess  of  HNO3  and  AgNO3,  and  titrate  excess  AgNO3  with  thio- 
cyanate  and  ferric  indicator. 

Silica  is  determined  by  evaporating  and  igniting,  and  filter- 
ing off  the  insoluble  residue.  The  latter  is  then  taken  up  with 
hot  dilute  HC1,  filtered,  and  the  residue  on  the  filter  again  strongly 
ignited  and  weighed  as  SiO2.  Silica  may  exist  in  suspension  as 
free  SiO2,  or  in  solution  as  a  silicate  of  an  alkali  metal. 

Calcium  and  magnesium  may  be  determined  in  the  filtrate 
from  the  silica  by  heating  to  boiling,  adding  ammonia  in  slight 
excess,  filtering  and  proceeding  as  described  in  previous  sec- 
tions. (See  above.) 

Sodium  and  Potassium.  —  As  a  check  on  the  direct  estimation 
of  these  elements,  it  is  desirable  to  convert  the  total  evaporated 
residue  into  chlorides  or  sulphates,  and  weigh  as  such.  Evap- 
orate to  dryness  and  ignite  sufficiently  to  render  SiO2,  Fe2O3,  and 
A12O3  insoluble.  Re-dissolve  residue  in  water,  filter,  add  HC1 
or  H2SO4,  and  re-evaporate  to  dryness.  Weigh  residue.  In 
cases  where  the  water  contains  no  sulphates,  hydrochloric  acid 
may  advantageously  be  used.  In  this  case  the  total  metals  may 
be  found  by  simply  titrating  the  chlorine  in  an  aliquot  part  of 

1  See  A.  H.  Low,  "Technical  Methods  of  Ore  Analysis,"  p.  71. 


ANALYSIS   OF  SUNDRY  MATERIALS  473 

the  dissolved  residue.  If  the  amounts  of  Ca  and  Mg  are  known, 
these  are  deducted,  together  with  the  total  chlorine  in  the  evap- 
orated residue;  the  balance  may  generally  be  taken  as  xNa  + 

yK. 

In  cases  where  sulphates  are  originally  present,  it  is  better 
to  use  sulphuric  acid.  The  Ca  and  Mg  are  calculated  to  CaSO4 
and  M'gSO4;  the  difference  gives  xNa2SO4  +  yK2SO4;  from  which 
Na  and  K  can  be  obtained  by  calculation.  The  sulphuric  acid 
is  determined  in  an  aliquot  part  of  the  dissolved  residue,  and 
calculated  to  SO4.  Deducting  this,  we  obtain  the  total  metals, 
and  deducting  Ca  and  Mg,  we  obtain  the  combined  weight  of 
Na  and  K.  It  is  rarely  necessary  to  make  separate  determina- 
tions of  Na  and  K.  If  required,  this  can  be  done  as  described  in 
Sections  I,  III,  and  IV. 

Iron  and  Alumina.  —  A  sufficient  quantity  of  the  water  is 
evaporated  with  HC1,  adding  a  little  HNO3  and  igniting  residue  to 
destroy  organic  matter.  The  residue  is  then  boiled  with  HC1, 
filtered,  and  the  filtrate  mixed  with  ammonia  in  slight  excess. 
After  again  boiling  it  is  filtered,  and  the  precipitate  ignited  and 
weighed  as  xFe2O3  +  yA!2O3.  If  iron  is  to  be  determined  sep- 
arately, instead  of  igniting  the  precipitate,  dissolve  in  HC1  and 
estimate  calorimetrically  with  thiocyanate.  (See  Section  I.) 

Organic  Matter.  —  Evaporate  at  150°  C.  and  weigh  residue. 
Ignite  gently  to  burn  off  carbonaceous  matter  without  decom- 
posing metallic  carbonates,  and  weigh  again.  The  difference  of 
the  two  weights-  gives  a  rough  idea  of  the  amount  of  organic 
matter  present. 

A  simple  test  may  also  be  made  as  follows :  *  A  flask  is  rinsed 
out,  first  with  sulphuric  acid,  then  with  pure  distilled  water.  A 
measured  volume  (100  to  250  cc.)  of  the  water  to  be  tested  is 
run  into  the  flask,  which  is  then  stoppered  and  heated  to  80°  C. 
Add  10  cc.  sulphuric  acid  (25  per  cent,  by  vol.)  to  which  enough 
KMnO4  has  previously  been  added  to  give  a  faint  permanent 
pink  tint.  Add  also  10  cc.  potassium  permanganate  (0.395 
gram  KMnO4  per  liter).  Allow  to  stand,  stoppered,  for  four 
hours,  then  add  a  little  KI  and  titrate  iodine  liberated,  repre- 
senting residual  KMnO4,  with  a  corresponding  thiosulphate  solu- 
tion, using  a  little  starch  indicator  at  the  finish. 

Ice.  KMnO<  consumed  =  0.0001  gram  available  oxygen. 
»  Sutton,  "Volumetric  Analysis,"  8th  edition,  p.  518. 


474  THE  CYANIDE  HANDBOOK 

A  rule 1  based  on    average   analyses  of    organic   carbon   in 
waters  gives  the  following  factors: 

Organic  carbon  =  O  absorbed  X  2.38  (for  river  water). 

=  O  absorbed  X  5.8    (for  deep  well  water). 

i  Ibid.,  p.  508. 


PART    IX 

METALLURGICAL    TESTS 

WE  will  now  describe  certain  operations  which  are  frequently 
necessary  in  controlling  the  work  of  a  cyanide  plant,  and  in 
determining  the  proper  conditions  of  treatment.  These  consist 
of  various  tests  arid  measurements  based  on  well-known  mathe- 
matical, physical,  and  chemical  principles,  but  distinct  from 
ordinary  analytical  processes,  and  may  be  roughly  described  as 
metallurgical  tests.  These  will  be  considered  under  the  follow- 
ing heads: 

I.    Density  determinations. 
II.    Acidity  and  alkalinity  tests. 

III.  Grading  and  screening  tests. 

IV.  Concentration  and  amalgamation  tests. 

V.   Cyanide  extraction  and  consumption  tests. 
VI.   Tables  and  formulae. 


SECTION  I 

DENSITY   DETERMINATIONS 

IN  cyanide  treatment  it  is  very  essential  to  have  as  exact  a 
knowledge  as  practicable  of  the  quantities  of  material  treated 
per  day  or  per  charge,  in  order  to  regulate  operations  and  to 
check  the  actual  recovery  of  values.  Differences  between  "theo- 
retical "  and  "  actual  "  extraction  may  often  be  traced  to  inaccu- 
rate estimates  of  the  quantities  treated.  In  the  case  of  crushed 
ore,  moderately  dry  tailings  and  similar  material,  this  may  be 
done  by  direct  weighing,  but  in  many  cases,  such  as  slime  pulp, 
it  is  practically  impossible  to  weigh  the  charge  in  bulk,  and  the 
weight  can  only  be  calculated  indirectly  after  ascertaining  the 
densities  of  the  pulp  and  of  the  dry  material. 

(a)  To  find  weight  of  a  given  volume  of  sand  or  similar  material. 

In  cases  where  it  is  not  convenient  to  weigh  the  entire  charge 
direct,  the  wet  and  dry  weight  of  a  charge  is  often  ascertained  by 
allowing  a"  vessel  of  known  capacity,  say  a  large  cubical  or  cylin- 
drical box,  to  be  filled  at  the  same  time  and  in  the  same  manner 
as  the  tank  or  other  container  in  which  the  material  is  to  be 
treated.  When  the  charge  is  completed,  the  surface  is  leveled 
off  without  pressing  down  and  the  box  and  contents  weighed  on  a 
platform  scale  or  suitable  balance.  The  entire  charge  is  also 
leveled  and  its  volume  computed  from  the  known  dimensions 
of  the  containing  vessel.  In  the  case  of  a  cylindrical  tank, 

V  (volume)  —  T  r*h. 

where  r  =  radius  of  tank. 

h  =  average  depth  charged  with  material. 

(22  \ 

=  -=-  approximately  J» 

In  the  case  of  a  conical  vessel, 


3 
where  r  =  radius  of  circle  forming  upper  surface  of  mass  of  material 

filling  cone. 
h  =  depth  from  surface  to  apex  of  cone. 


3.14159  f  =  y  approximately  V 


477 


478  THE  CYANIDE  HANDBOOK 

After  weighing  the  sample,  a  sufficient  quantity,  say  1  or  2 
kg.  (4  or  5  Ib.)  is  weighed  separately,  spread  out  in  a  thin  layer 
on  a  metal  tray,  and  dried  at  a  moderate  heat.  After  drying 
the  tray  and  contents  are  re-weighed  and  the  percentage  of 
moisture  calculated. 

The  wet  weight  of  the  charge  is  then  easily  calculated  as  fol- 
lows: 

Let  W  =  wet  weight  of  charge. 

v  =  volume  of  sample. 

w  =  wet  weight  of  sample. 

h  =  depth  charged  in  tank  (average). 

r  =  radius  of  tank. 
Then  v:irr*h:  :w:  W. 

w     "r*hw 
or  —r 

The  value  of  h  is  deduced  from  the  average  of  a  number  of 
measurements  taken  at  different  parts  of  the  surface  to  deter- 
mine the  depth  left  empty  between  the  top  of  the  tank  and  the 
charge. 

The  dry  weight  of  the  charge,  D,  is  calculated  from  p}  the  per- 
centage of  moisture,  as  follows: 

D:TT::100  -  p:  100 
or  D 

(b)  To  find  the  weight  of  a  given  volume  of  wet  pulp  (e.g., 
a  charge  of  slime). 

In  cases  where  the  material  is  of  such  a  nature  that  all  the 
interstices  between  the  particles  are  filled  with  liquid,  as  in  a 
charge  of  slime  mixed  with  water  or  cyanide  solution,  the  total 
dry  weight  may  be  calculated  from  the  following  data: 

V  =  total  volume  of  charge. 

P  =  density  (specific  gravity)  of  pulp. 

S  =  density  (specific  gravity)  of  the  dry  material. 

The  total  volume  (V)  is  determined  as  already  described,  from 
the  known  dimensions  of  the  containing  vessels.  We  may  define 
the  density  or  specific  gravity  of  a  substance  as  the  ratio  between 
its  weight  and  the  weight  of  an  equal  volume  of  water  at  a  tem- 
perature of  4°  C.  At  that  temperature  the  weight  of  1  cc.  of 
water  is  1  gram;  hence  the  density  of  any  liquid  or  solid  is  the 


DENSITY  DETERMINATIONS  479 

weight  in  grams  of  a  measured  quantity,  divided  by  the  number 
of  cubic  centimeters  which  it  occupies. 

The  density  of  the  pulp  is  determined  by  filling  a  vessel  of 
exactly  known  volume,  for  instance  a  liter  flask,  with  an  aver- 
age sample  of  the  pulp  and  weighing  its  contents.  The  volume 
of  the  containing  vessel  need  not  be  known,  if  the  weight  of  water 
filling  it  to  the  mark  be  ascertained.  In  this  case  a  correction 
is  required  for  the  expansion  of  water  if  the  determination  be 
made  at  any  other  temperature  than  4°  C.,  though  this  is  negli- 
gible for  most  practical  purposes. 

The  density  of  the  dry  substance  of  which  the  pulp  is  formed 
is  generally  found  by  weighing  a  certain  amount  of  a  carefully 
dried  average  sample,  placing  it  in  a  vessel  of  known  capacity 
and  filling  up  to  the  mark  with  distilled  water.  The  weight  of 
the  vessel  filled  with  water  alone  is  also  determined.  Before 
weighing  the  vessel  containing  the  material  and  water,  it  is  neces- 
sary in  some  cases  to  immerse  it  for  one  or  two  hours  in  boiling 
water  up  to  the  neck,  leaving  the  stopper  out,  to  allow  the  expul- 
sion of  any  air  contained  in  the  dry  powder.  It  is  then  cooled 
and  weighed.  The  density  of  the  dry  material  may  then  be  cal- 
culated as  follows: 

Let  m  -  weight  of  dry  substance  taken. 

a  =  weight  of  water  filling  vessel  to  mark  when  no  substance  is  added. 
6  =  weight  of  substance  together  with  amount  of  water  required  to 

fill  vessel  to  mark  after  substance  has  been  added. 
c,  =  weight  of  residual  water. 
d  —  weight  of  water  displaced  by  dry  material 
s  =  density  of  dry  material. 
Then  b  =  m  +  c 
d  =  a  —  c 

mm  m 

d       a  —  c      m  +  a  —  b 
Or  let  W\  =  weight  of  vessel  when  filled  with  water  to  mark. 

TF2  =  weight  of  vessel  with  dry  material,  filled  up  with  water  to 

mark. 

Wo  =  weight  of  empty  vessel 
Then      a  =  Wl  -  W0 
b=W2-W0 

m 

and  s  —  TIT ifr 

m   +   rr  i  —   rrj 

The  weight  of  dry  material  in  the  total  charge  may  then  be 
calculated  from  the  known  values  of  P  and  S. 


480  THE  CYANIDE  HANDBOOK 

Let  P  —  density  of  pulp. 

S  =  density  of  dry  material 
V  =  total  volume  of  pulp 
m  =  total  weight  of  dry  material  in  pulp 
c  =  weight  of  water  in  pulp 
w  =  weight  of  a  unit  volume  of  water 


From  (1)      c  =  VwP  -  m  From  (2)    c  =  -  ^— 

Hence         m  = 

This  formula  is  subject  to  the  same  correction  for  expansion 
of  water  which  is  involved  in  calculating  the  value  of  P. 
(c)  Useful  data  deducible  from  the  above  formula}.1 
(1)  Percentage  of  dry  material  in  a  charge  of  pulp. 

Let  p  =  percentage  of  dry  material 
Then  p:  100:  :  m:  m  +  c 

(100  -  p)m 
Hence  c  =  - — 

P 

,,        m  +  c     m  +  cS 
From  (1)  and  (2)  above:   Vw  =  — -p—  =  • — ^ — - 


and  p 


m  (S  -  P)    .  100  -  p          S-P 

S(P-l}'  henCG  —  F- 
100  S(P-  1) 


_ 

(2)  Percentage  of  solution  in  a  charge  of  pulp. 

q  =  percentage  of  solution 
100  QS  -P) 


*=       ~p= 

(3)  Ratio  of  solution  to  dry  material  (R). 

»<?_    S-P 

P~S(P-1) 

(4)  Volume  of  unit  weight  of  pulp  (v). 


m  +  c      wP 
(5)  Weight  of  unit  volume  of  pulp  (u\). 


c        „ 

=  wp 


1  For  a  full  decussion  of   this   matter  see  note   by  W.   A.  Caldecott,  "Proc. 
Chem.,  Met.  and  Min.  Soc.  of  S.  A.,"  II,  p.  102,  153,  and  837. 


DENSITY  DETERMINATIONS  481 

(6)  Weight  of  dry  material  per  unit  volume  of  pulp  (mj . 

m     wS(P-l) 
m=V=      5-1 

(7)  Volume  of  pulp  containing  unit  weight  of  dry  material  (vj. 

,     V         5-1 
m~  wS(P—  1) 

(8)  Total  weight  of  solution  in  charge  of  pulp  (c) . 

Vw(S-P) 


c  = 


S-  1 


(d)  Application  of  the  above  formulae  to  particular  cases. 

(1)  Weights  in  pounds  avoir.     Volumes  in  cubic  feet.  —  1  cu. 
ft.  of  water  =  62.5  lb. 

Hence  w  =  62.5 

62.5  F5(P-1) 

5—  1 

1  0.016 

62.5  P         P 
wl  =  62.5  P  =  (weight  of  a  cu.  ft.  of  pulp) 

62  5  5  (P 1) 

m1  =  — =  (weight  of  dry  material  per  cu.  ft.  of  pulp) 

o  —  1  . 

t  ^  0.016  (5—  1)  =  cu.  ft.  of  pulp  containing  1    lb.  of  dry 

S(P—  1)  material 

c  =  62.5  JOS- P)  =  lb  of  golution  in  y  (cu  ft  of  pulp) 
o  —  1 

(2)  Weights  in  tons  of  2000  lb.     Volumes  in  cubic  feet.  —  1  ton 
of  water  =  32  cu.  ft. 

Hence  w=  32 

32 


32(5-1) 

32  (S-  1) 

V       S(P-l) 

V(S-P) 

"  32(5-  1) 

VS(P-l) 
"    32(5-1). 


482  THE  CYANIDE  HANDBOOK 

(3)    Weights  in  metric  tons  of  1000  kilograms.     Volumes  in 
cubic  meters.  —  1  ton  of  water  =  cu.  meter. 


SECTION  II 

ALKALI  CONSUMPTION  TESTS 

IT  is  often  desirable  to  ascertain  by  preliminary  experiments 
the  quantity  of  alkali  which  will  be  needed  to  neutralize  acidity 
in  any  particular  ore.  In  this  connection  a  distinction  is  some- 
times made  between  "  free  "  and  "  latent "  acidity. 

The  free  acidity  is  that  due  to  substances  soluble  in  water, 
and  is  determined  by  agitating  a  known  weight  (say  half  a  pound 
or  200  grams)  in  a  closed  bottle  with  a  sufficient  quantity  of 
water  (say  4  or  5  parts  water  to  1  of  ore)  for  half  an  hour  or  so. 
After  settling,  filter  off  a  sufficient  portion  of  the  liquid,  take  an 
aliquot  part  (say  J  or  TV  of  the  whole  liquid),  and  determine  the 
acidity  by  titrating  with  standard  alkali.  In  some  cases  this 
acidity  may  be  determined  by  direct  titratiori  of  the  nitrate  with 
standard  caustic  soda  and  phenol-phthalein  indicator,  but  the 
results  are  usually  indefinite  owing  to  the  precipitation  of  metallic 
salts  which  obscure  the  end-point.  A  better  method  is  to  add 
a  decided  excess  of  alkali;  filter,  and  titrate  the  filtrate  or  an  ali- 
quot part  of  it  with  standard  acid,  using  one  or  two  drops  of  a  0. 1 
per  cent,  solution  of  methyl  orange  as  indicator. 

The  latent  acidity  may  be  taken  to  mean  the  consumption  of 
alkali  due  to  the  combined  effect  of  substances  insoluble  in  water. 
Thus  many  ores  contain  insoluble  sulphates  of  iron,  etc.,  which 
are  decomposed  by  lime,  caustic  soda,  etc.,  and  thus  neutralize 
alkali. 

The  total  acidity  (free  and  latent  together)  is  determined  by 
agitating  a  weighed  quantity  of  the  substance  with  an  excess  of 
standard  caustic  soda  or  clear  lime  water,  using  a  measured  quan- 
tity of  known  strength.  After  agitation  for  half  an  hour,  or  one 
hour,  the  liquid  is  filtered  and  a  measured  portion  titrated  with 
standard  acid,  using  methyl  orange  as  indicator.  A  convenient 
proportion  for  this  test  is  two  parts  liquid  to  one  of  ore.  The 
standard  alkali  solution  may  be  so  adjusted  that  the  consumption 

483 


484  THE  CYANIDE  HANDBOOK 

per  ton  of  ore  may  be  obtained  with  little  or  no  calculation. 
Thus,  if  200  grams  ore  be  used,  it  is  agitated  with  400  cc.  of  0. 1 
per  cent.  NaOH  or  CaO,  containing,  therefore,  0.4  gram  of  the 
alkali.  Say,  for  example,  that  100  cc.  of  the  nitrate  are  titrated 
and  that  V  cc.  of  standard  acid  are  required,  equivalent  to  V  cc. 
of  standard  alkali;  then  the  entire  400  cc.  of  liquid  would  have 
required  4  V  cc.,  equivalent  to  0.004  V  gram  alkali  remaining 
unconsumed.  The  alkali  consumption  is  therefore  0.4  —  0.004 
V  gram  on  200  grams  of  ore,  or  4  (1  -  0.01  7)  Ib.  per  ton  of  2000 
Ib. 

The  latent  acidity  may  be  found,  if  required,  by  taking  the 
difference  between  free  and  total  acidity.  It  should  be  remem- 
bered that  the  determination  must  generally  be  made  on  a  moist 
sample  of  material,  as  drying  vitiates  the  test  by  changing  the 
conditions.  It  must  therefore  generally  be  accompanied  by  a 
moisture  determination,  made  on  a  separate  portion  of  the  mate- 
rial, as  described  in  Section  I,  and  the  results  calculated  to  dry 
weight.  It  is  also  necessary  to  point  out  that  various  soluble 
salts  (ferrous  sulphate,  magnesium  sulphate,  alum,  etc.)  which 
are  not  in  themselves  acid  to  test  paper,  may  nevertheless  con- 
stitute the  whole  or  part  of  the  acidity  when  determined  as 
described. 

When  an  approximate  idea  of  the  acidity  of  an  ore  has  been 
obtained  by  tests  such  as  those  just  described,  it  is  often  possible 
to  determine  more  exactly  the  quantity  which  would  be  needed 
in  practice  by  agitating  or  percolating  a  number  of  equal  por- 
tions of  the  ore  with  water  to  which  different  amounts  of  lime 
or  caustic  soda  have  been  added.  By  this  means  the  minimum 
alkali  necessary  to  neutralize  acidity  may  be  ascertained,  the 
solution  drawn  off  from  each  test  being  titrated  with  standard 
acid.  When  lime  is  used,  sufficient  time  must  be  allowed  for 
the  reaction,  owing  to  its  slight  solubility  in  water. 


SECTION  III 

SCREENING   AND   HYDRAULIC  SEPARATION 

Screening  Tests.  —  Much  useful  information  may  frequently 
be  obtained  by  making  a  "grading  test"  or  "screen  analysis" 
of  the  ore  or  product  under  investigation.  If  such  tests  be  car- 
ried out  on  a  sample  of  ore  or  tailings  which  it  is  proposed  to 
treat  with  cyanide,  and  a  similar  set  with  the  residue  after 
treatment,  it  is  often  apparent  that  one  part  of  the  ore  is  more 
refractory  than  another,  and  it  may  be  seen  whether  it  would  be 
advantageous  to  separate  the  finer  and  coarser  particles  for  spe- 
cial treatment.  Thus,  if  it  be  found  that  the  extraction  is  more 
effective  in  the  finer  portions,  it  may  be  inferred  that  re-grinding 
of  the  coarser  particles  would  probably  result  in  improved  extrac- 
tion. The  efficiency  of  stamps,  ball-mills,  tube-mills,  and  other 
crushers  may  be  tested  with  more  or  less  accuracy  by  making 
screening  tests  on  the  products  entering  and  leaving  the  mill. 
(See  Part  III.) 

These  tests  are  made  by  passing  a  weighed  quantity  of  the 
dried  sample  successively  through  a  number  of  sieves,  and  weigh- 
ing separately  the  portions  retained  on  each  and  the  portion  which 
passes  through  the  finest  sieve.  The  material  is  made  to  pass 
through  the  sieve  by  gentle  rubbing,  at  the  same  time  shaking 
or  tapping  the  sieve,  taking  care  to  avoid  any  grinding.  The 
rubbing  may  generally  be  done  effectively  by  means  of  a  large 
cork  or  flat  block  of  smooth  wood.  If  necessary,  the  various 
products  are  separately  assayed,  and  the  percentage  of  the  total 
values  contained  in  each  may  be  calculated.  The  coarser  pro- 
ducts Should  be  re-ground  before  assaying,  so  that  average 
samples  may  be  taken.  In  most  cases  500  to  1000  grams  of  the 
original  material  will  suffice  for  a  set  of  grading  tests,  but  where 
the  particles  are  coarse  a  larger  amount  must  be  taken. 

The  particulars  of  a  test  of  this  kind  are  conveniently  sum- 
marized in  some  such  form  as  the  following,  which  is  given  merely 
as  an  example,  and  would,  of  course,  vary  according  to  circum- 
stances. 

485 


486 


THE  CYANIDE   HANDBOOK 


Total 
Weight 

Percent, 
of 

Assay  of  Product 
per  ton  of  2000  Ibs. 

Per  cent,  of 
Total  Values 

Product: 
Grams 

Total 
Weight 

Gold: 
dwt. 

Silver: 
dwt. 

Gold 

Silver 

(a)   Remaining  on  20-mesh 

(6)   Passing    20-mesh    and 

remaining  on  30-mesh 

(c)   Passing     30-mesh     and 

remaining  on  60-mesh 

(d)   Passing    60-mesh     and 

remaining  on  120-mesh 

(e)   Passing    120-mesh    and 

remaining  on  200-mesh 

(/)  Passing  200-mesh  

Hydraulic  Separation  Tests.  —  In  some  cases  it  is  essential 
to  make  the  separation  by  water,  as,  for  example,  when  it  is 
desired  to  ascertain  how  much  slime  would  be  obtained  from  a 
given  ore  after  crushing  in  a  given  manner.  Various  forms  of 
apparatus  are  in  use  for  sizing  and  screening  tests  by  hydraulic 
separation,  consisting  generally  of  conical  vessels  of  glass  or  other 
suitable  material,  arranged  so  that  a  regulated  jet  of  water  may 
be  introduced  at  the  apex  of  the  cone.  The  action  is  in  fact  an 
imitation  of  that  taking  place  in  the  spitzlutte  described  in  Part 
III. 

A  serviceable  practical  test  is  to  stir  a  known  weight  of  ma- 
terial in  a  bucket  with  4  or  5  times  its  weight  of  water,  allow  to 
settle  30  seconds,  1  minute,  2  minutes,  etc.,  according  to  the 
nature  of  the  material,  and  decant  the  bulk  of  the  liquid  and 
suspended  matter  into  a  larger  vessel.  This  operation  is  re- 
peated as  often  as  the  liquid  decanted  carries  any  appreciable 
amount  of  matter  in  suspension.  The  residue  in  the  bucket  is 
then  dried  and  weighed,  and  assayed  if  necessary,  and  the  whole, 
or  a  measured  average  part,  of  the  decanted  pulp  is  also  carefully 
dried,  weighed,  and  assayed.  If  the  density  of  the  pulp  and  of 
the  dry  material  contained  in  it  be  determined,  the  weight  of  the 
whole  may  be  determined  as  described  in  Section  I,  without  the 
necessity  of  drying  more  than  a  small  portion  of  the  decanted 
pulp.  Some  ores  contain  very  appreciable  amounts  of  soluble  mat- 
ter, of  which  due  account  must  be  taken  in  calculating  results. 


SECTION  IV 

CONCENTRATION  AND   AMALGAMATION  TESTS 

Concentration  Tests  are  made  with  a  prospecting  pan,  batea, 
vanning  shovel  or  similiar  appliance.  Considerable  skill  and 
practice  is  required  to  obtain  successful  results  or  to  imitate 
approximately  the  effect  of  large-scale  machinery.  For  hand 
panning  tests,  the  most  convenient  method  is  to  arrange  a  large 
bowl  or  bucket  of  enameled  iron  at  a  suitable  hight,  so  that  the 
pan  may  be  dipped  into  it  without  discomfort.  This  vessel  is 
partly  filled  with  clean  water  and  a  further  supply  of  water  from 
a  tap  or  another  bucket  should  be  close  at  hand.  The  weighed 
sample  (1  or  2  Ib.)  which  is  to  be  panned  is  taken,  a  handful  at 
a  time,  and  stirred  in  the  pan  with  a  little  water,  care  being  taken 
to  make  any  floating  particles  sink  as  much  as  possible  by  agita- 
ting the  surface.  The  pan  is  held  just  above  the  surface  of  the 
water  in  the  large  bucket,  and  the  lighter  particles  are  washed 
off  by  a  combined  shaking  and  revolving  motion,  dipping  the 
pan  occasionally  under  the  water,  brushing  off  the  "tail"  of 
light  sand  and  gradually  increasing  the  inclination  till  only  heavy 
mineral  remains.  -The  latter  is  then  washed  off  into  a  separate 
vessel,  and  a  fresh  handful  of  the  ore  taken  for  panning.  When 
the  whole  is  finished  it  is  generally  necessary  to  pan  the  concen- 
trates themselves  over  again  with  some  care.  These  are  then 
dried  and  weighed.  As  the  concentrates  frequently  contain 
much  pyrites  or  other  easily  oxidized  ingredients,  the  drying 
must  generally  be  done  at  a  low  temperature. 

The  results  may  be  conveniently  tabulated  in  much  the  same 
way  as  those  of  grading  tests.  The  following  shows  the  manner 
of  arranging  a  combined  concentration  and  hydraulic  separation 
test; 


487 


488 


THE  CYANIDE   HANDBOOK 


Product 

Total 
Weight 
of 
Product: 
Grams 

Per  cent, 
of 
Total 
Weight 

Assay  of  Product 
per  ton  of  2000  Ibs. 

Per  cent,  of 
Total  Values 

Gold: 
dwt. 

Silver; 
dwt. 

Gold 

Silver 

Concentrates       

Tailinffs  (s&nds) 

Slimes  

Amalgamation  Tests  are  designed  to  imitate  the  effect  of  plate 
amalgamation  after  crushing  with  stamps,  or  of  pan  amalga- 
mation in  Wheeler,  Huntington,  or  other  pans.  Many  methods 
have  been  proposed,  but  it  is  doubtful  if  any  of  them  are  reliable 
under  all  circumstances.  One  of  the  simplest  methods  of  obtain- 
ing an  approximation  to  the  results  of  plate  amalgamation  is  as  fol- 
lows: One  kg.  of  the  dry  ore  is  placed  in  a  large  wide-mouthed  jar 
together  with  500  cc.  of  water  and  (say)  5  grams  of  caustic  soda. 
After  agitating  and  ascertaining  that  the  charge  still  shows  dis- 
tinct alkalinity  to  litmus,  200  grams  of  mercury  are  added  and 
the  mixture  agitated  for  one  or  two  hours  by  rolling  the  closed 
bottle  up  and  down  on  a  table.  The  contents  are  then  washed 
out  into  an  enameled  bowl  or  other  suitable  vessel  and  the  mer- 
cury separated  by  panning.  In  cases  where  the  latter  has  been 
broken  up  into  small  globules  it  may  sometimes  be  collected  by 
adding  a  considerable  quantity  of  fresh  mercury,  or  by  rubbing 
with  a  little  sodium  amalgam,  caustic  soda,  or  ammonium  chloride. 
The  floured  mercury  may  also  be  re-united  by  addition  of  cya- 
nide, or  of  nitric  acid,  but  these  are  obviously  not  admissible  in 
a  test  of  this  kind. 

The  extraction  indicated  by  the  test  is  best  determined  by 
assays  of  the  ore  before  and  after  treatment;  results  based  on  the 
gold  found  by  dissolving  and  distilling  the  mercury  panned  off 
are  usually  unreliable,  as  losses  are  difficult  to  avoid  and  the 
mercury  employed,  if  not  specially  purified,  is  very  liable  to  con- 
tain gold  originally.  Attempts  are  sometimes  made  to  imitate 
the  conditions  of  plate  amalgamation  by  washing  the  ore  on  an 
amalgamated  copper  dish,  the  surface  of  which  is  kept  bright 
by  repeated  applications  of  cyanide  and  sal  ammoniac,  but  in 
the  writer's  experience  this  method  cannot  be  safely  relied  on. 
Agitation  in  a  bottle  with  sheets  of  amalgamated  copper  has  also 
been  tried,  but  cannot  be  recommended.  The  results  by  either 


CONCENTRATION  AND   AMALGAMATION  TESTS          489 

of  these  methods  are  liable  to  be  much  lower  than  those  obtained 
with  the  same  ore  on  a  working  scale. 

A  test  imitating  pan  amalgamation  may  be  made  by  grinding 
in  an  iron  mortar  300  to  500  grams  of  ore,  90  to  250  cc.  of  water, 
0.75  to  1.5  grams  caustic  soda,  and  30  to  100  grams  of  mercury. 

The  above  proportions  are  usually  suitable,  but  may  be 
varied  according  to  circumstances.  The  grinding  is  continued 
for  1,  2,  or  3  hours,  according  to  the  nature  of  the  material.  The 
mortar  is  then  emptied  into  a  dish  and  the  mercury  panned  off 
as  in  the  preceding  test,  and  the  residue  dried  and  assayed.  In 
cases  where  cyanide  tests  are  to  be  made  on  the  residue  after 
amalgamation,  the  latter  is  simply  allowed  to  drain  as  much  as 
possible  without  drying  over  a  fire. 


* 


SECTION   V 

CYANIDE  EXTRACTION   AND   CONSUMPTION  TESTS 

SMALL  scale  tests  are  often  of  the  greatest  utility  in  determin- 
ing the  proper  working  conditions.  There  are  cases  where  enor- 
mous unnecessary  outlay  has  been  incurred,  unsuitable  plants 
erected  or  processes  adopted,  through  the  neglect  of  a  few  simple 
and  comparatively  cheap  experiments  on  the  material  which  it 
was  proposed  to  treat.  Before  deciding  on  any  system  of  cyanide 
treatment,  the  following  points  should  be  elucidated  by  prelim- 
inary tests:  (1)  The  fineness  to  which  the  ore  should  be  crushed. 
(2)  The  strength  of  solution  in  cyanide  and  alkali  most  suitable 
for  the  conditions.  (3)  The  time  of  treatment.  (4)  The  best 
ratio  of  solution  to  ore.  (5)  The  necessity  or  otherwise  of  water- 
washing,  aeration,  oxidation,  roasting,  or  other  preliminary  or 
auxiliary  treatment.  It  is  supposed  that  some  idea  of  the  nature 
of  the  ore  has  already  been  obtained  by  following  out  the  tests 
described  in  previous  sections,  for  acidity,  concentration,  amal- 
gamation, etc. 

STANDARD  PRELIMINARY  CYANIDE  TESTS 

In  most  cases  the  following  test  will  yield  useful  information, 
which  may  be  employed  as  a  basis  for  further  investigations. 
A  carefully  selected  average  sample  of  the  ore  is  crushed  to  pass 
a  40-mesh  sieve.  The  following  mixture  is  then  charged  into  a 
well-stoppered  bottle:  Ore,  100  grams;  Lime,  1  gram;  Solution, 
100  cc.  containing  cyanide  equivalent  to  0.5  per  cent.  KCy  (0.5 
gram  KCy  or  0.377  gram  NaCy)-  For  very  poor  ores,  the  weights 
of  ore,  lime,  and  solution  should  be  increased  in  proportion.  The 
bottle  is  agitated  continuously  for  16  hours,  at  the  end  of  which 
time  it  is  allowed  to  stand  for  an  hour  and  a  sufficient  quantity 
of  the  supernatant  liquid  decanted  off  and  filtered.  The  filtrate 
is  tested  for  cyanide  and  alkali.  The  residue  in  the  bottle  is 
then  washed  out  into  a  large  enameled-iron  bucket,  well  stirred 

490 


CYANIDE  EXTRACTION  AND  CONSUMPTION  TESTS        491 

with  water,  and  washed  at  least  twice  by  decantation  with  a 
large  volume  of  water  so  as  to  remove  practically  the  whole  of 
any  soluble  matter.  If  the  nature  of  the  material  allows,  this 
washing  may  conveniently  be  done  on  a  vacuum  filter.  In 
either  case  the  washed  residue  is  dried  and  assayed. 

For  agitation  tests  of  this  kind  a  very  convenient  apparatus 
may  be  constructed  by  cutting  holes  of  the  size  and  shape  required 
to  receive  the  bottles  in  a  large  wooden  disk.  These  holes  should 
be  arranged  symmetrically  and  should  be  shaped  so  that  the 
stoppers  of  the  bottles  are  directed  towards  the  center  of  the  disk. 
Some  arrangement  must  also  be  provided  for  securing  the 
bottles  firmly  in  their  places.  The  disk  is  mounted  so  as  to 
revolve  in  a  vertical  plane  and  driven  at  a  moderate  speed. 
Where  such  apparatus  is  not  available,  the  bottles  may  be  securely 
wrapped  in  cloth  and  tied  to  the  spokes  of  a  flywheel  or  similar 
revolving  mechanism. 

The  results  of  this  test  will  give  an  approximate  idea  of  the 
extraction  likely  to  be  obtainable  by  ordinary  methods  of  treat- 
ment and  of  the  probable  consumption  of  chemicals.  The  ore 
is  assayed  before  and  after  treatment,  the  difference  of  the  assays 
giving  the  value  dissolved  per  ton.  The  difference  in  the  percent- 
age of  cyanide  in  the  solution,  before  and  after  treatment,  mul- 
tiplied by  20,  gives  the  consumption  of  cyanide  in  pounds  per 
ton  of  2000  lb.,  since  100  grams  of  ore  and  100  cc.  of  solution 
were  taken  for  the  test.  The  same  difference,  multiplied  by  10, 
gives  the  consumption  of  cyanide  in  kilos  per  metric  ton  of  1000 
kilos. 

TESTS  TO  DETERMINE  CONDITIONS  OF  TREATMENT 

Having  obtained  a  general  idea  of  the  behavior  of  the  ore 
to  wards/ cyanides  by  the  preceding  standard  test,  the  best  con- 
ditions may  be  more  precisely  determined  by  arranging  series 
of  tests  in  which  one  condition  is  varied  at  a  time.  The  follow- 
ing are  given  merely  as  examples,  and  would  of  course  be  varied 
according  to  circumstances. 


492  THE  CYANIDE  HANDBOOK 

(1)   Varying  fineness  of  ore: 

Weight  Weight       Lime        Cyanide           Time 

of  ore  of  solution   added :     strength :             of 

taken :  taken :                                           Agitation : 

grams  grams       grams   KCy  per  cent.      hours 

100  100              1                 0.5                   16 


in  each  case 


Tests  made  by  bottle  agitation,  as  described  above,  on  average 
portions  separately  crushed  to  30,  40,  60,  100,  150,  and  200- 
mesh. 

Let  it  be  supposed  that  the  results  show  little  or  no  advan- 
tage in  crushing  finer  than  60-mesh.  A  further  series  is  then 
arranged. 

(2)  Varying  strength  of  cyanide: 

"Ore         Mesh      Solution      Lime      Agitation 
..__  __      inn  °,  in  each  case 

100  grams         60      100  grams    1  gram     16  hours 

Cyanide  strength  in  different  tests  per  cent.,  0.05,  0.1,  0.2,  0.3, 
0.4,  0.5,  calculated  as  KCy. 

Supposing  the  extraction  to  be  sufficiently  complete  with 
0.2  per  cent.,  a  further  series  might  be  made  with  0.1,  0.125,  0.15, 
0.175,  and  0.2  per  cent.,  the  results  of  which  might  indicate  that 
there  is  no  advantage  in  increasing  the  strength  above  0.15  per 
cent.  =  3  Ib.  KCy  per  ton  of  ore  treated. 

(3)  Varying  alkali: 

Ore        Mesh     Solution         Cyanide          Time     1.         , 
100  grams      60     100  grams    0.15  per  cent.    16  hours  JIB 

Lime  added:  0.1,  0.2,  0.3,  0.4,  0.5,  0.7,  1,  1.5  grams.  Results 
indicate  that  0.2  gram  (=  4  Ib.  per  ton  of  ore)  is  sufficient. 

(4)  Varying  time  of  treatment: 
Ore        Mesh    Solution        Cyanide  Lime     1 . 

Mn  PAPn  Pflcjp 

100  grams      60          100        0.15  per  cent,     0.2  gram  / 
Time  of  agitation:  6,  9,  12,  16,  20,  24,  36,  48  hours. 

Let  it  be  supposed  that  the  tests  show  an  increased  extrac- 
tion up  to  36  hours.  A  further  series  may  be  made,  giving  24, 
27,  30,  33,  36  hours'  agitation.  Results  show  no  increase  of  ex- 
traction after  30  hours. 


CYANIDE   EXTRACTION  AND  CONSUMPTION  TESTS         493 

(5)  Varying  ratio  of  solution  to  ore: 

Ore      Mesh      Cyanide  Lime    Time  of  treatment  1  in  each 

100  grams     60    0.15  per  cent.    0.2  gram          30  hours         j    case 

Weight  of  solution  added:  75,  100,  125,  150,  200,  300  grams. 
Let  it  be  supposed  that  no  increased  extraction  is  obtained  by 
increasing  the  amount  of  solution  beyond  125  grams.  It  is  thus 
shown  that  the  most  suitable  proportion  is  1.25  tons  solution 
per  ton  of  ore. 

The  indications  obtained  by  these  tests  may  then  be  con- 
firmed by  experiments  on  a  larger  scale,  in  which  the  ore  is  treated 
by  some  system  of  percolation  or  agitation,  imitating  working 
conditions  as  closely  as  practicable. 

Percolation  Tests  are  usually  made  on  a  scale  of  1  to  25  Ib. 
(500  grams  to  10  kg.)  For  this  purpose  it  is  very  convenient  to 
use  stoneware  jars  having  an  outlet  at  the  bottom,  a  wooden 
frame  covered  with  cotton  cloth,  and  a  glass  outlet  tube  passing 
through  a  well-fitting  cork  or  rubber  stopper.  The  filter-frame 
should  be  arranged  so  as  not  to  leave  too  large  a  space  between 
it  and  the  bottom  of  the  jar,  and  the  space  between  the  edges 
of  the  frame  and  the  sides  of  the  jar  should  be  tightly  tamped  with 
twine  or  other  packing.  By  means  of  a  short  length  of  rubber 
tube  and  a  screw-clip  the  outflow  of  solution  can  be  regulated  at 
will.  If  preferred,  wooden  buckets  may  be  used  instead  of  jars, 
but  if  allowed  to  dry  when  not  in  use,  these  may  give  trouble 
by  leakage.  A  trover  is  advisable,  to  prevent  access  of  dust, 
etc.,  and  to  check  undue  evaporation. 

The  treatment  is  as  nearly  as  possible  that  which  would  be 
given  in  a  leaching  tank  on  a  working  scale.  An  average  sample 
is  well  mixed,  with  addition  of  the  necessary  quantity  of  lime,  as 
indicated  J®y  previous  experiments.  Solutions  are  added  at 
suitable  intervals,  using  for  each  solution  from  one-tenth  to  one- 
fifth  of  the  dry  weight  of  ore  treated,  giving  strong  and  weak 
solutions  as  described  in  Part  IV,  and  regulating  the  strength 
of  solution  and  time  of  treatment  in  accordance  with  the  results 
already  obtained  in  the  bottle  tests.  After  sufficient  contact 
with  the  ore,  the  solutions  are  drawn  off  slowly  by  slightly  un- 
screwing the  clip.  The  outflowing  liquor  is  received  in  a  jar  or 
bottle  and  should  be  measured  and  tested  for  cyanide  and  alkali. 
If  a  complete  record  of  these  solution  tests  be  kept,  a  very  fair 


494  THE  CYANIDE  HANDBOOK 

estimate  may  be  made  of  the  probable  cyanide  consumption  in 
practice. 

When  the  treatment  is  complete,  the  whole,  or  an  average 
sample  of  the  residue  is  dried  at  a  low  temperature  and  assayed. 
It  is  often  instructive  to  compare  the  result  of  this  assay  with 
that  of  a  similar  portion  of  the  residue  which  is  thoroughly  washed 
with  water  before  drying.  The  washing  may  generally  be  done 
on  a  vacuum  filter. 

Aeration  Tests.  —  Where  compressed  air  is  available,  these 
may  be  very  effectively  carried  out  by  using  glass  vessels  which 
terminate  at  the  bottom  in  a  sharply  pointed  cone,  at  the  apex 
of  which  the  air  is  introduced,  the  pressure  being  regulated  by  a 
tap  or  by  a  screw-clip  on  a  short  length  of  very  stout  rubber 
tubing.  The  conical  bottom  avoids  the  possibility  of  any  material 
settling  and  escaping  agitation.  A  fairly  satisfactory  apparatus 
may  be  improvised,  where  compressed  air  is  not  available,  by 
using  a  large  jar  filled  with  water  as  an  aspirator,  and  connecting 
this  with  the  agitation  apparatus  in  such  a  way  that  a  current  of 
air  is  drawn  through  the  latter.  The  apparatus  is  of  course 
not  continuous,  as  the  aspirator  has  to  be  refilled  from  time  to 
time. 

When  a  test  is  to  be  made  the  mixture  of  ore  and  solution  is 
charged  into  the  vessel  with  conical  bottom  and  the  current  of 
air  passed  at  regulated  speed  through  the  pulp  as  long  as  may 
be  necessary.  Comparative  tests  under  varying  conditions  may 
be  arranged,  on  similar  lines  to  the  bottle  tests  above  described. 
A  comparison  between  these  aeration  tests  and  the  agitation  tests 
made  in  closed  bottles  will  show  whether  aeration  is  advantageous 
or  otherwise. 

Other  Small-scale  Tests.  —  Many  other  experiments  in  connec- 
tion with  cyanide  treatment  are  at  times  required,  to  elucidate 
such  points  as  the  following:  (1)  Use  of  preliminary  water-wash 
or  acid  treatment.  (2)  Use  of  artificial  oxidizing  agents,  either 
in  preliminary  treatment  or  as  adjuncts  to  cyanide.  (3)  Use  of 
bromocyanide,  ferricyanide,  or  other  auxiliary  dissolving  agent. 
(4)  Necessity  or  otherwise  of  roasting  previous  to  cyanide  treat- 
ment. (5)  Combination  of  cyanide  treatment  with  amalgama- 
tion, concentration,  chlorination,  or  other  mechanical  process. 


CYANIDE  EXTRACTION  AND  CONSUMPTION  TESTS        495 

TABULATION  OF  RESULTS 

The  following  are  the  principal  data  which  should  be  recorded, 
though  of  course  the  details  may  vary  according  to  circumstances: 
Weight  of  ore  taken  for  test  (wet). 
Weight  of  ore  taken  for  test  (dry). 
Moisture  (per  cent.). 
Mesh  to  which  ore  is  crushed. 
Time  of  treatment  (hours):  (a)  agitation: 


(b)  percolation: 

(c)  settlement: 


total: 


Proportion  of  solution  to  dry  ore. 
Strength  of  solution  used  in  cyanide 


average  KCy  per  cent, 
maximum  KCy  per 


cent. 

Strength  of  solution  in  alkali,  calculated  as  NaOH. 
Consumption  of  cyanide:  Ib.  per  ton. 
Consumption  of  lime:  Ib.  per  ton. 
Assay  value:  (a)  original,     (b)  residue. 
Extraction :  (a)  dwts.  or  grams  per  ton.     (b)  per  cent. 


SECTION   VI 

USEFUL   FORMULA 

(1)  To  find  weight  of  cyanide  (or  other  soluble  salt)  to  be 
added  for  making  up  stock  solution  to  required  strength. 

When  the  solutions  are  contained,  as  is  usually  the  case,  in 
cylindrical  or  rectangular  tanks,  the  quantity  is  calculated  by 
measuring  the  depth  in  the  tank,  having  previously  determined 
the  weight  corresponding  to  a  unit  of  depth. 

Let  D  =  total  depth  of  solution  in  storage  tank  when  filled  to  required 
point. 

d  =  depth  in  storage  tank  already  filled 

a  =  per  cent,  of  cyanide  at  present  in  storage  tank 

6  =  per  cent,  of  cyanide  in  sump  or  reservoir  from  which  liquid  is  to  be 
drawn  in  making  up. 

p  =  percentage  required  in  final  solution 

t  =  weight  of  solution  corresponding  to  unit  depth  in  storage  tank. 

Then  D  —  d  =  depth  of  solution  to  be  added  to  storage  tank 
x  =  weight  of  solid  cyanide  to  be  added. 

(D  —  d}  t  =  weight  of  solution  to  be  added 

~  -  —  ^      =  weight  of  cyanide  in  solution  to  be  added 

•       •  =  weight  of  cyanide  in  solution  already  present  in  storage  tank 
100 

Dp.t  =  weight  of  cyanide  in  solution  as  finally  prepared 
"100 

Then  Dp'1     x  I  dat 

1  ~  x  + 


100  100  100 

_  Dt(p-  b)-  dt(a~  b) 
100 

Where  the  weight  of  solution  is  given  in  tons  of  2000  Ib.  and 
the  weight  of  cyanide  in  Ib.  av.,  the  formula  becomes 

a;  =20   [Dt(p-b)-dt(a-  6)  j 

Where  the  weight  of  solution  is  given  in  metric  tons  of  1000 
kg.  and-  the  weight  of  cyanide  in  kg.,  the  formula  becomes 

x=  10 

496 


USEFUL   FORMULAE  497 

Illustrations.  —  (a)  The  storage  tank  is  of  such  a  diameter 
that  1  inch  in  depth  corresponds  to  2.5  tons  of  solution.  The 
total  depth  is"  8  feet  (i.e.,  96  in.),  and  it  is  filled  with  cyanide  solu- 
tion of  0.19  per  cent,  strength  to  a  depth  of  3  ft.  2  in.  (=  38  in.). 
It  is  required  to  fill  the  storage  tank  from  a  sump  containing  0.08 
per  cent,  solution.  What  quantity  of  solid  cyanide  must  be 
added  to  give  a  solution  of  0.20  per  cent.  KCy? 

Here  D  =  96;  d  =  38;  t  =  2.5;  p  =  0.2;  a  =  0.19;  and  b  =  0.08 
Hence  x  =  20  )  240  X  0.12  -  95  X  0.11 }    =  367  Ibs. 

(b)  The  storage  tank  is  of  such  a  size  that  1  cm.  in  depth 
corresponds  to  0.4  ton.  The  total  depth  is  2  in.  50  cm.  (=  250 
cm.).  The  solution  contained  is  of  0.22  per  cent,  strength,  and 
it  is  required  to  make  it  up  to  0.25  per  cent,  from  another  reser- 
voir containing  solution  at  0.13  per  cent.  The  present  depth 
in  the  storage  tank  is  1  m.  10  cm. 

Here  D  =  250;  d  =  110;  a  =  0.22;  b  =  0.13;  p  =  0.25;  and  t  =  0.4. 
Hence  x  =  10  j  100  X  0.12  -  44  X  0.09 }  = 
=  80.4  kg. 

(2)  To  find  the  strength  of  resulting  solution  when  two  solu- 
tions of  different  strength  are  mixed. 

A  =  weight  of  first  solution  (in  tons,  Ibs.  kilos,  etc.) 
B  =  weight  of  second  solution  (in  same  units) 
a  =  per  cent,  of  cyanide  or  other  ingredient  in  first  solution 
b  =  per  cent,  of  same  in  second  solution 
p  =  per  cent,  in  mixture 
Then  y^r  =  weight  of  ingredient  in  first  solution 

•QT 

___  =  weight  of  ingredient  in  second  solution 

- —        ^=  weight  of  ingredient  in  mixture 

Aa       Bb  _(A  +  B)p  Aa  +  Bb 

100  *  100          100""    >r  P  ~    A  +  B 

(3)  To  find  weight  of  one  solution  which  must  be  added  to 
another  to  make  it  up  to  required  strength. 

Using  same  symbols  as  above, 

orB=^n4A 


498  THE  CYANIDE  HANDBOOK 

(4)  Formulae  for  converting  percentages  into  results  per  ton. 

P  =  percentage 

20P  =  Ib.  av.  per  ton  of  2000  Ib. 
22.4  P  =  Ib.  av.  per  ton  of  2240  Ib. 

10P  =  kg.  per  ton  of  1000  kg.  =  grams  per  kg. 


L^.  p  =  iip  p  =  oz.  Troy  per  ton  of  2000  lb. 
oz.  Troy  per  ton  of  2240  lb- 
dwt.  per  ton  of  2000  lb. 
-P  =  dwt.  per  ton  of  2240  lb. 

CONVERSION  OF  METRIC  WEIGHTS  AND  MEASURES 

APPROXIMATELY 

1  meter  =    39.370432  inches  =  39.4 

=      3.280869  feet  =    3.3 

"  =      1.093623  yard  =    1.1 

1  inch  =      2.539977  centimeters  =    2.54 

1  foot  =      0.304797  meter  =    0.3 

1  yard  =      0.914392  meter  =    0.9 

1  cubic  meter        =    35.3156  cubic  feet  =  35.3 

1  liter  =    61.0254  cubic  inches  =  61 

"  =      0.035316  cubic  feet  =  ^ 

1  cubic  foot  =      0.0283161  cubic  meters  =  ^ 

1  gram  =    15.43234874  grains  =  15.4 

"  =      0.643015  dwt.  =  | 

=      0.032151  oz.  Troy  =  & 

1  kilogram  =      2.20462125  lb.  av.  =2.2 

1  grain  =      0.06479895  gram  =  0.065 

1  dwt.  =      1.555176  gram  =  1£ 

1  oz.  Troy  =  31.10352  grams  =  31 

1  lb.  Av.  =  453.592652  grams  =  454 

1  ton  of  1000  kg.  =  2204.621  lb.  Av.  =  2205 

1  ton  of  2000  lb.    =  907.185  kilograms  =  907 

1  ton  of  2240  lb.    =  1016.048  kilograms  =  1016 
1  gram  per  ton  of  1000  kg.  =14  grains  per  ton  of  2000  lb. 
1     "        «     «             «     «     =  _^  dwt.       tt     it  «     <t 

1     "        "     " .  «     "     __     •    O7         tt     tt  a    tt 

1  dwt.  per  ton  of  2000  lb.     =  ty  gram  per  ton  of  1000  kg. 
1  oz.  per  ton  of  2000  lb.          =  -^  grams  per  ton  of  1000  kg. 

MISCELLANEOUS  DATA 

1  ton  of  2000  lb.  =  291 66f  oz.  Troy 

1  lb.  Av.  =  14.58333  oz.  Troy 

1    "      "  =  W  oz.  Troy  =  1^  dwt.  =  29 If  dwt. 


USEFUL   FORMULAE 


499 


1  Ib.  Av. 
1  oz.  Troy 
1  oz.  Av. 

1  Ib.  per  ton  of  2000  Ib. 
1  kg.  per  ton  of  1000  kg. 


1  Ib.  Av.  of  water 
1  gallon  of  water 
1  gallon  (U.  S)  of  water 
1  cubic  foot  of  water 


'  7000  grains 

480  grains 
:  437.5  grains 

0.05  per  cent. 

0.5  kilo  per  ton  of  1000  kg. 

0.1  per  cent. 

2  Ib.  per  ton  of  2000  Ib. 

27.68122  cubic  inches 
10  Ib.  =  276.8122  cubic  inches 
8.345  Ib.  =  231  cubic  inches 
62.425  Ib.  =  62^  approx. 


ATOMIC  WEIGHTS  (1909) 


Aluminum    Al 

Antimony Sb 

Argon   A 

Arsenic As 

Barium Ba 

Bismuth Bi 

Boron    B 

Bromine Br 

Cadmium    Cd 

Caesium    Cs 

Calcium    Ca 

Carbon    C 

Cerium    Ce 

Chlorine    Cl 

Chromium    Cr 

Cobalt "...  .Co 

Columbium    Cb 

Copper    Cu 

Dysprosium Dy 

Erbium Er 

Europium Eu 

Fluorine    .  .  .S. F 

Gadolinum Gd 

Gallium . .  Ga 

Germanium    Ge 

Glucinum Gl 

Gold    Au 

Helium He 

Hydrogen H 

Indium In 

Iodine I 

Iridium  .  .  .Ir 


27.1  Iron Fe       55.85 

120.2  Krypton Kr       81.8 

39.9  Lanthanum    La  139 

75.0  Lead   . Pb  207.1 

137.37  Lithium    Li          7 

208  Lutecium   Lu  174 

11  Magnesium Mg      24.32 

79.92  Manganese Mn      54.93 

112.40  Mercury   Hg  200 

132.9  Molybdenum   Mo      96 

40.09  Neodymium Nd  144.3 

12  Neon Ne      20 

140.25  Nickel. Ni       58.68 

35.46  Nitrogen N        14.01 

52.1  Osmium    Os  190.9 

58.97  Oxygen O         16 

93.5  Palladium Pd  106.7 

63.57  Phosphorus    P        31 

162.5  Platinum    Pt  195 

167.4  Potassium    K        39.1 

152  Praseodymium Pr  140.6 

19  Radium    Ra  226.4 

157.3  Rhodium    Rh  102.9 

69.9  Rubidium , Rb      85.45 

72.5  Ruthenium Ru  101.7 

9.1  Samarium Sa  150.4 

197.2  Scandium Sc       44.1 

4  Selenium Se        79.2 

1.008  Silicon Si        28.3 

114.8  Silver    Ag  107.88 

126.92  Sodium Na      23 

193.1  Strontium .  .Sr        87.62 


500 


THE  CYANIDE  HANDBOOK 


Sulphur S  32.09 

Tantalum Ta  181 

Tellurium Te  127.5 

Terbium Tb  159.2 

Thallium Tl  204 

Thorium Th  232.42 

Thulium Tm  168.5 

Tin    Sn  119 

Titanium    .  .  .Ti  48.1 


Tungsten    W  184 

Uranium U  238.5 

Vanadium    V         51.2 

Xenon Xe  128 

Ytterbium    Yb  172 

Yttrium    Y        89 

Zinc Zn       65.37 

Zirconium Zr        90.6 


INDEX 


PAGE 

Aaron,  C.  H.,  assay  of  pyritic  ores 362 

Abosso  Gold  Mining  Co.,  flux  for  zinc 

precipitate    267 

Absorption  of  solution  by  wooden  vats  199 

Accumulation  of  zinc  in  solutions 39,  256 

Accumulations  of  tailings,  handling  of  159 

Acid  radicals,  estimation  of,  in  cyanide  456 

in  solutions    440 

Acid-treated  precipitate,  composition  of  263 

Acid  treatment  of  concentrates    194 

of  cupriferous  ores 310 

of  zinc-gold  precipitate 41,  123,  261 

use  of  sodium  bisulphate  in    123 

Acidity  of  ores,  estimation  of 483 

of  water,  estimation  of 468 

Aeration  of  slime  pulp 210 

tests 494 

Agitation  by  air 210 

by  mechanical  stirrers    208 

by  pumps 210 

process  of  cyanide  treatment.  .33,  36,  208 

Alexander,  F.,  stamp  milling  practice .  144 

Alkali  consumption  tests    483 

estimation  of,  in  solutions 451 

in  water 468 

hydrates,  estimation  of 451 

influence  of,  in  zinc  precipitation  . .  249 

on  extraction 109 

Alkali-metal  cyanides,  properties  of  . .  65 

Alkali  metals,  estimation  of    397 

Alkali,  strength  required  in  slime  treat- 
ment      257 

washes  in  sand  treatment 201 

use  of,  in  cyanide  process 27,  201 

All-sliming  process 283 

Alloys,  analysis  of 430 

Aluminium,  estimatio/f'of,  in  ores,  etc.  .  398 

in  water 473 

precipitation  with 122 

use  of,  as  anode 303 

Amalgam,   method   of   obtaining  from 

plates 181 

Amalgamation,  conditions  of  good  .  180, 181 

cyanide  as  an    aid    to 21 

cyanide  in,  of  concentrates    16 

effect  of  fine  crushing  on 144 

metals  on 182 

minerals  on    182 

films  on  plates  in 182 


PAGE 

Amalgamation,  foreign  matter    intro- 
duced during 185 

in  relation  to  cyaniding 179 

inside 180 

pan    180 

plate    180 

previous  to  cyanide  treatment 34 

use  of  chemicals  in 183 

use  of  cyanide  in 14,  21, 184 

Ammonia,    estimation    of,    in    cyanide 

solutions 451 

manufacture  of  cyanide  from    "130 

use   of,    as    preliminary   solvent   for 

cupriferous  ores 112,  311 

Ammonium  argentocyanide    76 

compounds,  estimation  of 451 

manufacture  of  cyanide  from    ...  130 

Ammonium  cyanide,  preparation  of    .  64 

properties  and  reactions 64 

Ammonium,  cyanides  of  copper  and  .  78 

estimation  of,  in  cyanides    460 

in  solutions    451 

thiocyanate    100 

Analytical  operations 393 

Andreoli,  E.,  peroxidized* lead  anodes.  300 

Annealing  cornets  in  bullion  assay    . .  383 

Anodes  in  electric  precipitation 121 

in  Siemens-Halske  process 299 

iron 121,  299,  300 

peroxidized  lead   121,  300 

Anticipation  of  cyanide  process   10-24 

Antimonial  ores,  assay  of 366 

Antimony,  effect  of,  in  amalgamation  182 

in  zinc  precipitation    254 

estimation  of 399, 400 

separation  of 399 

Argall,  P.,  conditions  of  zinc  precipi- 
tation      119 

modern  practice  with  rolls 146 

nature  of  zinc-box  deposits 254 

power  required  for  Ball  mills   154 

roasting  furnace    288 

rolls H8 

Argentic  cyanide 74 

Argentocyanic  acid 76 

Argento-potassic  cyanide    75 

Arrastra    150 

Arsenic  detection  of 403 

estimation  of 401 


501 


502 


INDEX 


Arsenic  in  amalgamation   182 

in  zinc  precipitate 123,  254 

separation  of 402 

Arsenical  ores,  assay  of    365 

cyanide  treatment  of 295 

Artificial  oxidizers,  use  of,  in  cyaniding  103 

Ash,  estimation  of,  in  coal    466 

Assay,  arrangement  of    339 

balance,  adjustment  of 347 

crucible  fire 333,  354 

of  antimonial  ores    366 

of  arsenical  ores 365 

of  basic  ores   358 

of  battery  scrapings 376 

of  cupels 374 

of  cupriferous  ores 367 

of  gold  and  silver  bullion    378 

of  graphite  crucibles    354 

of  lead  ores 365 

of  pyritic  concentrates 361 

of  pyritic  ores 360 

of  refractory  materials    371 

of  siliceous  ores 333,  355 

of  slags 373 

of  telluride  ores    369 

of  zinc  ores 365 

quantities  of  flux  in    335 

quantities  of  ore  in 333 

scorification    349 

silver,  by  volumetric  methods 389 

special  methods  of 349 

weights,  accuracy  of   386 

Assaying 315 

with  metallic  iron    362 

with  niter 363 

Atomic  weights  (1909)    499 

Auriammonic  cyanide    74 

Auriargentic  cyanide 74 

Auric  cyanide    72 

Auripotassic  cyanide    73 

thiocyanate    101 

Aurisodic  thiocyanate    101 

Auropotassic  cyanide 73 

thiocyanate    101 

Aurosodic  cyanide    73 

Aurous  cyanide 72 

double 72 

Automatic  lime  feeder 178 

pulp  distributor    166 

sampler 319 

Auxiliary  dissolving  agents    293 

Bagration,  Prince  P.;  solubility  of  gold 
in  potassium  cyanide  and  ferro- 

cyanide 10 

Balbach  Smelting  and  Refining  Co., 
treatment  of  zinc-gold  precip- 
itate    272 

Ball  mills  . .  152 


PAGE 

Ball  mills,  power  required  for 154 

Banket  ore,  use  of  in  Tube  mills .  .  156,  157 
Banks,    E.    G.,    grading    test    of    tube 

mill  product 157 

Barium  argentocyanide 76 

cyanide 68 

estimation  of 404 

Barker,    H.    A.,  precipitation  in  pres- 
ence of  copper 120 

precipitation  of  copper  from  cyanide 

solution  by  means  of  acids  ....  312 
Base  metal  compounds,  action  of,  on 

cyanide 110 

Base  metals,  estimation  of,  inbullion  .  .  433 

Basic  ores,  assay  of 358 

Battery  practice 143, 180 

scrapings,  assay  of 376 

Bay  and    Prister,     analysis    of    white 

precipitate    119 

Begeer,    B.    W.,    assay    of    low    grade 

samples 356 

quartz  ores 355 

fluxing  of  zinc  precipitate    267 

Belt  concentrating  tables    190 

conveyors 167 

Bergman   and   Guyton,    researches   on 

prussic    acid    4 

Beringer,  C.  and  J.  (text  book  of  assay- 
ing), assay  of  basic  ores 358 

cyanide  tailings 357 

siliceous  ores 355 

estimation  of  arsenic 402 

copper 411 

iron    414 

lead 415 

manganese    418 

mercury    418 

tin    426 

separation    of    gold    and    silver    in 

bullion  by  means  of  cadmium  431 

Berthelot,  cyanide  chemistry 9 

Berthollet,  chloride  of  cyanogen 5 

composition  of  prussic  acid 5 

Berzelius,  cyanide  chemistry 9 

Bertram  Hunt  filter   233 

use    of    ammonia    in    treatment    of 

cupriferous  ore    313 

Bettel  and  Marais,  effect  of  oxidizers  on 

cyanide  extraction    103 

Bettel,    W.,    reaction    of    oxygen    and 

cyanide  on  gold    102 

Bicarbonate  of  soda,  use  as  flux 335 

Bicarbonates,  estimation  in  cyanide    .  456 

in  solutions    448 

in  water 469 

Bismuth,  effect  of,  in  amalgamation  . .  182 

estimation  of 405 

Black    Hills    (South  Dakota),    Merrill 

filter  press  at    220 


INDEX 


503 


PAGE 

Black  Hills,  system  of  treatment  at  .  .  284 

zinc-dust  precipitation  at 306,  308 

Blake  crusher 135 

Blake-Marsden  crusher   135 

Blaisdell  excavator 207 

Blanketings   187 

Bodlander,  reaction  of  gold  and  cyanide.  102 

Bonanza  mine,  Tavener's  process  at.  .  272 
Bosqui,  F.  L.,  absorption  of    solution 

by  wooden  vats    199 

Butters  filter  press  costs    225 

Merrill  filter  press 221 

Bromide  of  cyanogen,  action  of,  on  gold 

and  silver 59 

action  of,  on  metals    59 

on  cyanide 59 

mono-    , 57 

physical  properties  of    58 

polymer  of 59 

preparation  of 57 

reactions  of    58 

Bromocyanide    practice    in    W.    Aus- 
tralia   295 

process    295 

Brown,  F.  C.,  air-lift  agitator 211 

R.  Oilman,  cyanide  practice    with 

the  Moore  filter 222 

W.  S.f  treatment  of  cupriferous  ores  310 

Brunton,  W.,  traveling  belt  filter    . . .  226 

D.  W.,  theory  of  sampling    320 

Bryan  mill 150 

Buckboard 323 

Buddies 187 

Bueb ,  J . ,  process  of  cyanide  manufacture  131 

Bull,  Irving  C.,  estimation  of  lead  .  . .  415 

Bullion,  analysis  of    430 

assay  of  gold  and  silver 378 

corrections  in  assay . , 387 

from  cyanide  process 42,  274 

smelting  of 270 

volumetric  assay  of  silver  in 389 

Bunsen,  R.  W.,  manufacture  of  cyanide 

from  atmospheric  nitrogen  ....  128 

Butters  and  Mein,  automatic  distributor  166 

Butters,  Charles,  bottom  discharge  door  206 

deep  tanks  fot^slime  settlement 214 

filter 224 

intermediate  collecting  tanks 166 

reverberatory    furnace    for    smelting 

zinc  precipitate 268 

Robinson  slime  plant    221 

sheet  lead  anodes \  .  300 

Butters   Copala   Syndicate,    slime    fil- 
tration    225 

Cadmium,  estimation  of 405 

use  of,  in  separating  gold  and  silver  .  431 
Calcium     cyanide,     preparation     and 

properties 69 


PAGE 

Calcium,    estimation    of,    in    metallic 

products 434 

in  ores 406 

in  solutions    446 

in  water « 472 

separation  of 405 

Calculation  of  cyanide  analyses 461 

of    tank  contents    477 

of  sand  charges 477 

of  slime  pulp  densities    479 

of  specific  gravities    479 

of  strength  of  solutions    496 

Caldecott,    W.   A.,    alkali   strength   of 

slimes  solutions 257 

circular  vats  for  zinc  precipitation  245 

influence  of  strength  of  solution  ...  108 

roasting  zinc  precipitate  with  niter.  264 

slime  pulp  formulae    480 

Caldecott,  W.  A.,  and  Johnson,  E.  H.f 
precipitating     surface     of     zinc 

shavings    250 

use  of  lead-zinc  shavings 253 

Callow  cone  settling  tank    176 

screen    •-. 161 

Calorific  power  of  coal,  estimation  of  466 

Cams 138 

Cam-shaft 138 

Carbon,  estimation  of,  in  coal    466 

organic,  estimation  of,  in  water  . . .  473 

Carbonaceous  residues,  assay  of 377 

Carbonate  of  ammonia,  use  of,  in  con- 
junction with  cyanide 22 

of  copper,  action  of,  on  cyanide    . .  112 

of  soda,  use  as  assay  flux 335,  357 

use  as  flux  for  zinc  precipitate  . .  125 

Carbonates,  estimation  in  cyanide    . .  456 

solutions 448 

water 469 

Carbonic  acid,  action  on  cyanide  ....  109 

estimation  in  ores    407 

water 469,  471 

Carter,  T.  L.,  assay  of  graphite  crucibles  354 

fluxing  of  zinc  precipitate   266 

lead  acetate  drip    249 

zinc-lead  couple    247 

Cassel  filter 225 

gold  extracting  process 24 

H.  R.,  colorimetric  estimation  of  gold  445 

Castner,  manufacture  of  cyanide  ....  130 

Cathodes,  amalgamated  copper 303 

in  electric  precipitation 121 

in  Siemens-Halske  process   121,  299 

lead 121,300 

tinned  iron 121,  301 

Caustic  lime,  estimation  of 464 

Caustic  soda,  use  of,  in  amalgamation .  184 
Central    City    (S.    Dakota),    crushing 

with  cyanide  solution 281 

Charcoal  precipitation 122,  308 


504 


INDEX 


PAGE 

Charcoal,   use    as  reducing    agent    in 

assaying    334 

Checks,  for  bullion  assays 380 

Chemical  losses  of  zinc 255 

Chemistry 45 

of  dissolving  process    102 

of  precipitation  process 117 

of  smelting  process    124 

Chilian  mill   149 

Chloride  of  cyanogen    5,  56 

gaseous 56 

solid 57 

Chloride   of    sodium,    use    of,   in    con- 
junction with  cyanide 21 

Chlorides,  estimation    of,  in    solutions  449 

Chlorine,  estimation  of,  in  ores    407 

in  solutions    449 

in  water 472 

Christy,     S.    B.,     charcoal     precipita- 
tion   308 

electrochemical    order    of    metals    in 

cyanide  solutions    106 

electromotive    force    of    minerals    in 

cyanide  solutions    106 

estimation  of  gold  in  solutions  ....  443 
precipitation  of  cyanide  solutions  by 

cuprous  salts 123,  309 

Chromicyanides 94 

Chromium,  cyanides  of 71 

estimation  of 408 

Chromocyanides 94 

Clancy,    continuous    system    of    slime 

settlement 215 

Clarification    of    solutions    before    pre- 
cipitation     38-236 

Clarifying  tanks 236 

Clark,  Thos.  C.,  patent 21 

Classifiers,  hydraulic    34, 172 

Claudet,  A.  C.,  cupellation  of  bullion    .  .  381 

platinum  parting  apparatus 384 

surcharge  of  bullion  assays    387 

Clean-up  of  zinc-boxes 258 

Clean-up  tanks 259 

Clevenger,   G.   H.,   treatment   of   zinc- 
gold  precipitate  with  litharge .  .  272 
Clouet,  artificial  production  of  cyanides 

from  ammonia 6 

Coagulating  agents,  for  settling  slimes .  .  177 

Coal,  analysis  of 465 

estimation  of  ash  in    466 

of  calorific  power  of    466 

of  carbon  in    466 

of  iron  and  phosphorus  in 467 

of  moisture  in 465 

of  sulphur  in 466 

of  volatile  matter  in 465 

Cobalt,  cyanide  of 71 

estimation  of 409 

Cobalticyanides  and  cobaltocyanides  .  94 


PAGE 

Cobar  (N.  S.  W.),  treatment  of  cuprif- 
erous ores  at 310 

Collecting  tanks 166 

Collection  of  sands  by  direct  filling    .  165 

by  intermediate  filling 166 

slimes    35,  208 

Colorimetric  estimation  of  chromium  408 

of  copper    412 

of  gold 445 

of  iron 414 

of  selenium 423,  450 

of  sulphides 449 

of  thiocyanates 442 

of  titanium 427 

Combination  mill  (Nevada),  slime  treat- 
ment      225 

Commercial  cyanide,  analysis  of    ....  455 

sampling  of 455 

Complex    cyanogen    radicals,    metallic 

compounds  of    84 

Comet  crusher    135 

Concentrates,     amalgamation     of,     by 

aid    of    cyanide 16 

cyanide  treatment  of 193 

Concentrating  tables 187 

Concentration  by  oil     191 

definition  of 186 

general  principles  of    185 

in  relation  to  cyanide  treatment    .  .  185 

previous  to  cyanide  treatment    ....  192 

tests 487 

Concentrators,  belt    190 

Buddie    187: 

modern  types  of 188 

old  types  of 187 

percussion 188 

Wilfley    188 

Conditions,  affecting  size    of    product 

in  Stamp  mills 141 

determining    separation   of   particles 

in  a  flowing  stream    172 

for  coarse  crushing 141 

for  effective  percolation    200 

for  good  precipitation 38,  248 

Cone  classifiers 175 

calculating  volume  of    477 

Conical  slime  treatment  vats    211,  284 

Coning  and  quartering 317 

Consumption  of  cyanide,  causes  of  . .  108 

tests  to  determine    490 

Consumption  of  zinc 41 

Conveyors     163,  164,  167,  171 

Copper,   action  of,  in  zinc  precipitation  120 

and  ammonium,  double  cyanides  of  78 

and  potassium,  double  cyanides  of . .  79 

anodes,  amalgamated 303 

compounds,  action  of,  on  cyanide   .  Ill 

cyanides  of 76 

detection  of  . .                                      .  409 


INDEX 


505 


PAGE 

Copper,  double  cyanides  of   78 

use  as  solvents 311 

estimation  of,  in  ores,  etc 411 

in  solutions    446 

ferricyanides 92 

ferrocyanides 88 

ores,  treatment  of    301 

removal    of,    before    cyanide    treat- 
ment     112,  310 

separation   of,   in   analysis..- 410 

Cornets,  gold,  annealing  of -  383 

treatment  of,  in  assaying 384 

Corrections  for  bullion  assays 387 

Costs     of     treatment     with     Butters' 

filter 225 

Cowper-Coles,  S.,  aluminium  cathodes  .  303 
Cripple  Creek  (Colo.),    crushing    with 

rolls 154 

assay  of  telluride  ores  from 370 

Croghan,  E.  H.,  analysis  of  lime 464 

composition  of  commercial  lime  .  .  .  463 
Crosse,   Andrew   F.,   assay  of  battery 

scrapings 376 

assay  of  graphite  crucibles 375 

slime-treatment  process 211 

Crown  mine  (Karangahake,  New  Zea- 
land),crushing  with  cyanide  solu- 
tion    281 

early  cyanide  trials  at    30 

Crucible  fusions 337,  354 

Crucibles  for  assays 336 

Crush  filters,  fixed  immersed   type . . .  220 

traversing  type   226 

Crushing  fine,  effect  on  amalgamation.  144 

machinery 135 

of  ores  as  affecting  cyanidation.  .  . .  143 

samples  for  analysis 395 

for  assay ~ 323 

Crushing  with  cyanide  solution    281 

advantages  of    281 

objections  to 282 

Black  Hills  practice 284 

Mexico  practice 285 

Nevada  practice 284 

Rand  practice 282 

United  States  practice    284 

Gumming,    A.    C.,    and    Masson,  O., 

estimation  of  cyanates    458 

Cupellation  assays 340 

of  bullion 381 

details  of 342 

effect  of  temperature  in 342 

losses  of  gold  and  silver  in 342,  380 

of  lead  from  treatment  of  zinc  pre- 
cipitate    272 

Cupels 340 

assay  of    374 

making  bone  ash    340 

size  and  form  of   341 


PAGE 

Cupric  cyanide,  preparation  and  prop- 
erties    77 

ferricyanide    92 

Cupriferous  ores,  assay  of 367 

difficulties  in  treatment  of 310 

preliminary  acid,  treatment  of 310 

use  of  ammonia  in  treating 313 

Cuproso-cupric  cyanides 77 

Cuprous  cyanide,  preparation  and  prop- 
erties   76 

ferricyanide    92 

salts,  precipitation  by 123,  308 

Cut  samples  of  bullion     378 

Cyanamides  as  intermediate  products 

in  cyanide  manufacture    129 

Cyanates,  action  of  acids  on 97 

estimation  of 457 

general  properties  and  reactions  of  .  .  96 

metallic 96 

of  potassium   97 

of  silver    97 

Cyanic  acid,  discovery  of 8 

preparation  and  properties 96 

Cyanicides 108 

Cyanide,  as  aid  to  amalgamation    ...  14,  21 

as  solvent  with  other  chemicals  ...  22 

as  solvent  of  metallic  sulphides ....  16 

extraction  tests 490 

in  conjunction  with  electric  current.10,  15 

manufacture  of 9, 127 

relative  solubility  of  metals  in 17 

solubility  of  gold  in 6 

solubility  of  silver  in 20 

solutions,  analysis  of 437 

use  of,  in  amalgamation 14, 183 

Cyanide  process,  early  history  of  ....  3 

importance  of,  in  metallurgy 31 

introduction  of    30 

later  developments  of 31 

outline  of  operations  in    33 

stages  of 33 

Cyanides,  artificial  formation  of 6 

Proust's  researches  on    6 

metallic 62 

Cyanippus  filter  press 217 

Cyanogen,  action  of  acids  on ...  50 

action  of  alkalis  on 50 

action  of  metals  on 49 

bromide  of 57 

chemical  characteristics  of 48 

Cyanogen  compounds,  early  use  of  . .  3 

estimation  of 440 

with  non-metals 47,  56 

Cyanogen,  Davy's  researches  on 8 

estimation  of 434 

in  cyanide    456 

formation  of    47 

Gay-Lussac's  researches  on    7 

physical  properties  of    . 48 


506 


INDEX 


PAGE 

Cyanogen,  Proust's  researches  on  ....  '7 

reactions  of    49 

use  of,  in  gold  extraction 26 

Cyanurates 98 

Cyanuric  acid 98 

Daniell,  J. ,  scorification  in  fusion  furnace  353 

theory  of  scorification 352 

Davy,  Sir  H.,   discovery  of  iodide  of 

cyanogen 8 

electrolysis  of  hydrocyanic  acid    ...  54 

researches  on  cyanogen 8 

Decantation  of  solution  from  slime     .  .  209 

process    36,  209 

defects  of 213 

treatment  of  slimes 212 

Decomposition    of     cyanide    by     car- 
bonic acid    109 

by  copper  salts Ill 

by  external  influences 108 

by  iron  salts 110 

by  oxygen    109 

by  sulphides    113 

determination  of 490 

Deep  tanks  for  slime  settlement    '214 

Dehne  filler  press 217 

Deloro   mine   (Ontario,   Canada),   bro- 

mocyanide  treatment  at 295 

zinc-dust  precipitation  at 306 

Deniges,  G.,  estimation  of  silver 433 

Denny,  G.  A.,  sampling  of  ore  in  mine.  321 
G.  A.  and  H.  S.,  crushing  with  cyan- 
ide solution    282 

Density  determinations  of  sand 477 

of  slime 478 

Deposits  in  zinc-boxes    118,  252 

in  electric  precipitation 121,  299 

Desert   mill    (Nevada),  cyanide    prac- 
tice at 284 

Deutsche   Gold-Silber  Scheide-Anstalt, 

process  of  cyanide  manufacture  130 

Dewey,  F.  P.,  losses  in  cupellation.  .  .  344 

Diehl  process 295 

Diesbach,  discovery  of  Prussian  blue .  .  3 

Dilute  solutions,  claim  for  use  of 26 

selective    action  of 107 

Dip  samples  of  bullion 378 

Direct  cyanide  treatment 170,  279 

Direct  filling  of  sand  tanks 165 

Discharge  doors  for  cyanide  tanks    . .  200 

Butters 206 

James    206 

Discharging  residues    206 

from  bottom  of  tank 206 

from  side  of  tank 206 

Disposal  of  residues 38,  167,  206 

solutions   39,  235 

Dissolved  solids,  estimation  of,  in  solu- 
tions   .                              453 


PAGE 

Dissolving  process    33,  102,  195 

tanks 202,  236 

Distributor     for    charging    pulp    into 

tanks 166 

Dittmar  and  MacArthur,  estimation  of 

potassium 422 

Dixon,  Clement,  details  of  filler  press 

construction  and  practice 217 

Dixon,  W.  A.,  action   of   oxidizers   on 

metallic  gold  in  cyanide  solution .  18 
precipitation  of  gold  from     cyanide 

solutions 19 

treatment  of  pyritic  ores  with  cyano- 
gen compounds  and  oxidizers.  .  18 

Dodge  crushers 135 

Donath,  E.  and  Margoshes,  B.  M.,  es- 
timation of  ferrocyanides 435 

Double  treatment 166,  205 

Dowling,  W.  R.,  tube  mill  practice 155 

Drill  samples  of  bullion 378 

Drip  of  cyanide  at  head  of  zinc-boxes  .  .  249 

of  lead  acetate  in  zinc-boxes 249 

Drucker,  A.  E.,  treatment  of  matte.  .  .  271 

Dry  crushing 279 

advantages  of    280 

Duflos,  Dr.,  early    cyanide    extraction 

experiment 12 

Durant,   H.   T.,   estimation  of  gold  in 

solutions 444 

suction  valve  on  centrifugal  pump.  .  210 

Dures,  R.,  assay  of  battery  scrapings.  .  376 

assay  of  graphite  crucibles 375 

Early  cyanide,  extraction  test    12 

history  of  the  cyanide  process    3 

use  of  cyanogen  compounds 3 

use  of  suction  filters 208 

Edwards'  roasting  furnace 286 

Ehrmann,  L.,  sampling  slimes    332 

Electric  current,  influence  of,  on  extrac- 
tion  10,15 

precipitation,  advantages  of 40 

Siemens -Halske  process 40,  121,  289 

Electrochemical    order    of    metals     in 

cyanide  solutions, 18,  106 

Electrolysis  of  cyanide  solutionslO,40,121,  298 

Elkington's  process  of 10 

Rae's  process  of 15 

Electrolytic  processes 10,  40,  121,  298 

recent  developments  of 300 

Electromotive  order  of  metals  in  cyanide  18 

of  minerals  in  cyanide    106 

Electro-zinc  process 303 

Elkington,  J.  R.,  and  H.,  patent 10,  298 

Ellis,  C.  J.,  estimation  of  cyanurates.  .  441 

oxalates 452 

sulphides 450 

urea 452 

Elmore  oil  concentration  process 191 


INDEX 


507 


PAGE 

Eisner,  L.,  classification  of  metals  by 

their  reactions  with  cyanide ....  12 
influence  of  oxygen  in  action  of  met- 
als on  cyanide 11 

Eisner's  equation    102 

Endlich  and  Muhlenberger,  alleged  an- 
ticipations of  cyanide  process ...  23 
Erlwein    and    Frank,    manufacture    of 

cyanide 129 

Eschka,'  determination   of   sulphur    in 

coal    466 

Evans-Waddell  Chilian  mill 149 

Everitt,  action  of  acids  on  ferrocyanides  9 

Excavator,  Blaisdall 207 

Extraction  by  cyanide  process    38 

by  successive  decantations 213 

effect  of  oxidizers  on 103 

influence  of  solution  strength  on    . .  108 

tests  to  determine    490 

Faraday,  M.,  researches  on  solubility  of 

gold-leaf  in  cyanide 13 

Faucett,  H.  J.,  patent    21 

Feldtmann,  W.  R.,  double  treatment  of 

tailings    205 

Feldtmann,  W.  R.,  and  Bettel,  W.,  con- 
stitution of  cyanates 97 

Ferricyanide  of  copper    92 

of  iron 92 

of  potassium 90 

properties  and  reactions 91 

of  silver    93 

Ferricyanides,  characteristic  colors  of  90 

estimation  of 442 

use  as  auxiliary  solvents    294 

gold  solvents 104 

Ferrocyanide,  ferric 89 

of  hydrogen v 88 

of  potassium    86 

of  sodium 89 

of  zinc 89 

Ferrocyanides,  action  of  acids  on  ....  9,  85 

action  of  HsS  on    85 

characteristic  insoluble    87 

cuprous  and  cupric    88 

discovery  of  /('. 4 

electrolysis  of    7, 85 

estimation  of 435 

in  cyanide    459 

estimation  of,  in  solutions 441 

general  characteristics 85 

of  copper   88 

Porrett's  researches  on 7 

Proust's  researches  on     6 

solvent  action  of,  on  gold 10 

Ferroso-ferric  ferricyanide 92 

Ferrous  ferricyanide 92 

ferrocyanide 88 

potassium  ferrocyanide 88 


PAGE 

Ferrous  salts,  action  of,  on  cyanide    .  Ill 

Films,  on  amalgamated  plates     182 

Filter  cloths 199 

frames 199 

Filtering  slimes 216,  221 

Filter  plates,  construction  of 222 

Filter  presses 37, 216 

capacity  of 220 

clarifying  solution  by    236 

cyanippus 217 

Dehne 217 

details  of  construction 217 

general  principles  of    216 

Merrill 220 

method  of  discharging 220 

method  of  filling 219 

•treatment  of  slime  in    220 

use  of  compressed  air  with 220 

washing  cakes  in    220 

Filter  pressing  of  ore  slimes    37,  216 

of  zinc-dust  precipitate     307 

of  zinc-gold  precipitate 260,  262 

Filters,  Bertram  Hunt    233 

Brunton 226 

Butters 224 

Crush 226 

Moore 222 

Ridgway 230 

Filtration  by  pressure 216 

by  suction    221 

of  slimes 37,  216 

vacuum 221 

Fine  crushing,  for  cyanide  treatment. 37, 154 

grinding,  advantages  of    208 

metal,    in     assaying,     cleaning    and 

weighing 344 

Finkener,    method    for    estimation    of 

potassium 422 

Flint  mill    37 

Florence  (Colorado),  acid  treatment  of 

zinc  precipitate  at 262 

Flotation  process  of  concentrating  ore .  192 

Fluorine,  estimation  of 413 

Fluor-spar,  use  of,  as  flux 125 

Fluxes,  acid  and  basic 334 

for  crucible  assays 334,  355 

for  free-milling  ores 355 

for  smelting  cine  precipitate 124,  266 

quality  of  assay 335 

standard  (for  siliceous  ores)    334 

Formulae  (useful)    496 

Frankland,  growth  of  cyanide  indus- 
try    31 

Free  cyanide,  estimation  of 438 

influence  of,  on  zinc  precipitation .  .  248 

Frenier  spiral  sand  pump 169 

Fresenius,  C.  R.  (quantitative  analysis), 

estimation  of  cyanogen 435 

Frue  vanner    l&l 


508 


INDEX 


PAGE 

Fulminates 98 

Fulton,  C.  H.,  assay  of  siliceous  ores.  .  355 
and  Crawford,  C.  H.,  assay  of  zinc- 
box  precipitate 376 

Furnace,  Argall 288 

Edwards 286 

Merton 287 

Furnaces  for  roasting  ores 286 

for  roasting  zinc  precipitate    268 

revolving  cylindrical    288 

with  revolving  rabbles    286 

Fusion  in  hot  crucibles 339 

in  muffle 338 

of  zinc  precipitate    42,  268 

process  for  assays 337 

with  excess  of  litharge    361 

with  niter,  for  zinc  precipitate 270 

Fusions,  pouring,  in  assaying 338 

Gates,    rock-breaker 136 

Gay-Lussac,  analysis  of  cyanogen    ...  7 

prussic  acid 7 

assay  of  silver 389 

Gaze,  W.  H.,  proportion  of  zinc  required 

per  ton  of  solution    250 

George  and  May  mine  (Johannes- 
burg) ,  direct  treatment  of  coarse- 
crushed  ore  at 171,  279 

Gernet,  A.  von,  electrolytic  precipita- 
tion   40,298 

electrolytic  precipitation  on  mercury  303 

introduction  of  the  electric  process.  .  40 

losses  of  gold  in  mill  water 184 

treatment  of  cupriferous  ores 311 

Gilmour- Young  process 122,  304,  306 

Glassford    and    Napier,    researches    on 

cyanides  and  double  cyanides.  .  11 
Glenn,      W.,      sizes      allowable      with 

samples  of  different  weights .  .  .  320 

Gold,  action  of  cyanide  on 73,  102 

analysis  of  bullion 431 

assay  of,  in  ores,  tailings,  etc 315 

bullion  assay 378 

coated,  in  amalgamation 183 

cyanides 71 

cyanides  of,  and  ammonium 74 

and  potassium 73 

and  silver,  researches  on    4,  11 

and  sodium 73 

estimation  of,  in  solutions 443 

leaf,  experiments  on  action  of  cyanide 

with 13 

loss  of,  in  mill  water 184 

;      thiocyanates  of,  and  potassium 101 

Gopner,  production  of  bromocyanide .  .  58 
.Gowland,    W.,    surcharge    in    bullion 

assays    387 

.Grading  tests 485 

of  Ball  mill  products 154 


PAGE 

Grading  tests  of  Rolls  products 147 

of  Tube  mill  products 157 

reporting 486 

Graham,    K.    L.,    comparative   test   of 

banket  and  pebbles  in  Tube  mill  157 

Graphite  crucibles,  crucible  assay  of  ...  375 

scorification  assay  of 354 

use  of,  in  smelting    268 

Great    Boulder    mine    (W.  Australia), 

Ridgway  filter  at 232 

Green,  L.  M.,  estimation  of  protective 

alkali 439 

estimation  of  alkaline  hydrates  ....  451 

Grinding  machinery 146 

mills 148 

Grizzly    141 

Gross,  J.,  fluxing  of  zinc  precipitate.  .  .  267 

Growth  of  cyanide  industry 31 

Gyratory  crushers     136 

Hagen,  solubility  of  gold  in  cyanide ...  6 
Hahn,  H.  C.,  cyanide   as  a  solvent  of 

metallic    sulphides 16 

Haloid  cyanogen  compounds,  discovery 

of 5,  9 

estimation  of 441 

preparation  and  properties 56 

use  of,  in  cyanide  process 59,  295 

Hall  and  Popper,  assay  of  zinc  ores .  .  .  365 
Hamilton,  E.  M.,  practice  with  Butters 

filter 224 

Hammering  lead  buttons   338 

Handling  of  material  for  cyanide  treat- 
ment      159 

of  old  accumulations  of  tailings 159 

of  residues 206 

of  solutions 235 

Handy,  J.  O.,  volumetric  estimation  of 

magnesium 416 

Hannan's    Star    Mill     (W.  Australia), 

bromocyanide  practice  at 297 

Hardness  of  water,  estimation  of 471 

Harvey,  A.,  sampling  of  ore 319 

Heat   of   combination   of   metals   with 

oxygen 125 

Heating  solutions 239 

Herting,  O.,  estimation  of  cyanates    .  457 
Hillebrand  and  Allen,  action  of  nitrous 

acid  on  gold    347 

assay  of  cupels 374 

slags  from  telluride  ore 374 

telluride  ores 369 

losses  in  cupellation 342 

Hirsching,    H.,    use    of     ammonia    in 

treatment  of  cupriferous  ores.  .  311 

History  of  cyanide  process    3 

of  Mac  Arthur-Forrest  discovery.  ...  24 
Hogenraad,   G.   B.,  fluxes  for  siliceous 

ores    . .                                             .  356 


INDEX 


509 


PAGE 

Hood  process    297 

Hose  filling  of  sand  tanks 165 

Hot  solutions,  advantages  of 106 

tests  made  with 239 

Hunt  filter 233 

Huntington  mill 150 

improved    151 

Hydrates,  estimation  of,  in  cyanide   .  .  456 

in  water 470 

Hydraulic  classification 34,  172 

classifiers 172 

separation  tests 485 

Hydrochloric  acid,  use  of,  in  treating 

zinc  precipitate 262 

Hydrocyanic  acid 51 

action  of  acids  on    54 

action  of  alkalis  on 54 

action  of  metallic  salts  on  . 55 

action  of  non-metals  on 54 

action  of  oxides  on    55 

antidote  for 55 

electrolysis  of    54 

estimation  of 440 

occurrence  of,  in  nature 53 

physical  properties  of    53 

poisonous  nature  of 55 

polymer  of 55 

preparation  of 51 

reactions  of    54 

synthesis  of 52 

Hydroferricyanic  acid    92 

Hydroferrocyanic  acid 88 

Hydrogen,  ferricyanide  of    92 

evolution  of,  in  zinc  precipitation .  .  .  252 

evolution  of,  in  zinc  precipitation .  .  .  252 

ferrocyanide  of    88 

Hydrogen  peroxide,   occurrence  of,   as 
intermediate  product  in  reaction 

of  cyanide  on  gold 102 

Hydrolysis  of  cyanide 108 

Immersed  type  of  vacuum  filter    ....  229 
Indicators,  action  of    acids  and  alkalis 

on 468 

Intermediate  filling  of  sand  tanks 166 

Inquartation  .  .^ 345 

Insoluble  matter  in  cyanide,  estimation 

of  . 461 

Iodide  method  of  copper  assay 411 

Iodide  of  cyanogen,  discovery  of 8,  9 

preparation  and  properties  of 59 

reactions  of    60 

Iodine  method  of  zinc  estimation    .  .  .  447 

Iron  anodes 121,  299 

cathodes  (tinned)   121,  301 

compounds,  action  of  cyanides  on  .  110 

cyanogen  radicals 85 

estimation  of,  in  ores,  etc 414 

in  bullion  .  .  .433 


PAGE 

Iron,  estimation  of,  in  coal    467 

in  solutions    447 

in  water 473 

ferrocyanides 88 

group,  cyanides  of 71 

pyrites,  action  on  cyanide 110 

salts,  action  on  cyanide 110 

separation  of 413 

tanks 197 

use  of,  in  assaying 362 

Ittner,  researches  on  prussic  acid    ...  7 
Ivanhoe  Gold    Corporation,    bromocy- 

anide  practice 296 

James,  Alfred,  discharge  door 206 

influence  of  foreign  salts  on  precipi- 
tation with  zinc 249 

Janin,  Louis,  Jr.,  alleged  anticipitation 

of  cyanide  process 23 

criticism  of  cyanide  process 23 

solubility  of  silver  in  cyanide  .....  105 
Jarman  and  Brereton,  use  of  ammonia 
as  auxiliary  solvent  in  cyanide 

treatment 313 

Jaw  crushers 135 

Jenkens,   H.   C.,   antidote  for  cyanide 

poisoning    55 

Jennings,  Hennen,  hose  filling  of  tanks  166 
Joannis,    chemistry    of    cyanide    com- 
pounds      47 

electrolysis  of  ferrocyanide 86 

Johnson,  E.  H.,  stamp  milling  in  rela- 
tion to  cyaniding 144 

Johnson,  E.  H.,  and  Caldecott,  W.  A., 

fluxing   of   zinc-gold   precipitate  267 
Julian,  H.  F.,  reaction  of  cyanide  on 

gold 104 

Julian,  H.  F.,  and  Smart,  E.,  "Cyanid- 
ing Gold  and  Silver  Ores"  au- 
tomatic lime  feeder 178 

Ball  mill  practice 153 

Butters  filter-beams 225 

coagulating  agents  for  slime   177 

composition  of  ferric  hydrate    Ill 

discharge  doors  for  leaching  tanks  .  200 

excavators  for  discharging  tanks    .  .  207 

experiments  on  hot  solutions 239 

falling  particles  in  water,  laws  of    .  173 

filter  press  practice 220 

fluxing  of  zinc  precipitate    266 

leaching  vats 197 

Merton  furnace,  details  of 288 

sand  pumps 170 

slimy  sand,  treatment  of 160 

zinc-box  construction 245 

Kalgurli  (Kalgoorlie,  W.  Australia),  Ball 

mill  practice  at 154 

bromocyanide  practice  at 295 


510 


INDEX 


PAGE 

Karangahake  (New  Zealand),  establish- 
ment of  cyanide  process  at,  in 
1889 30 

Keith  and  Hood,  use  of  mercuric 

chloride  as  auxiliary  solvent.  .  .  297 

Kendall  process 293 

Knublauch,  manufacture  of  cyanides 

from  coal-gas 131 

Krupp-Grusonwerk  Ball  mill 153 

Lake  View  Consols,  filter  presses  at  .     219 

Lamb,  M.  R.,  agitation  with  air 210 

Latent  acidity 483 

Lay,  Douglas,  electrolytic  processes .  .  .     303 

Leaching,  definition  of    195 

process    200 

(see  also  Percolation,  tank) 
Lead  acetate,  use  of  in  precipitation .  .  .     249 

buttons,  scorification  of 353 

treatment  of,  in  assay 338 

cathodes 121,  300 

cyanides  of 83 

double  cyanide  of,  and  zinc 83 

effect  of,  in  amalgamation 182 

estimation  of 415,  433 

in  solutions    448 

ores,  assay  of    365 

peroxidized,  use  of,  for  anodes  ....      121 

separation  of 414 

smelting  of  zinc  precipitate .  .  42,  1'25,  272 

zinc  couple 38,  246 

Leaves,  vacuum  filter 225 

Leggett,  T.  H.,  fluxing  of  zinc  precipitate    267 
Lenssen     and     Mohr,     estimation     of 

ferrocyanides 442 

Lime,  analysis  of 463 

composition  of  commercial 463 

effect  of,  in  amalgamation 177,  183 

feeder,  automatic 178 

use  of,  in  preparatory  treatment  of 

slimes    177 

use  of,  in  settling  slimes    177 

Liners  for  graphite  crucibles 267,  268 

for  Tube  mills 154,  158 

Liquation  of  gold  in  bullion  bars    .  .  .     275 
Lisbon-Berlyn    mine,  direct  treatment 

of  coarsely  crushed  ore  at 279 

zinc-lead  couple  at 247 

Litharge,     smelting     zinc     precipitate 

with 42,125,272 

use  of,  in  assaying 335 

Lodge,  R.  W.,  assay  of  cupels 374 

assay  of  cupriferous  ores    368 

zinc-box  precipitate 350 

Loevy,  Dr.  J.,  assay  of  graphite  cru- 
cibles    375 

estimation  of  sulphides 450 

limits  of  scoriScation  assay 354 

Long  Tom 187 


PAGE 

Losses  in  cupellation 342,  380 

in  roasting  zinc  precipitate 264 

of  gold  in  mill  water    184 

of  zinc  in  cyanide  process 255 

Low,  A.  H.,  "Technical  Methods  of  Ore 

Analysis  "  estimation  of  antimony  400 

arsenic 402 

chlorides 472 

coal    466 

manganese    417 

potassium 421 

Lowles,  J.  T.,  charcoal  precipitations .  .  .  308 

Lxihrig  Vanner    191 

Luipaard's     Vlei     Estate,     details     of 

double  treatment  at 205 

MacArthur-Forrest  process    24 

amended  claim  for 27 

first  patent 25 

history  of  discovery 24 

introduction  of    30 

second  patent    27 

use  of  alkalis  in 27 

MacArthur,  J.  S.,  influence  of  ammonia 

in  cyaniding  cupriferous  ores    .  313 

lead-zinc  couple    246 

selective  action  of  dilute  solutions  .  26 

researches  on  gold  solvents 24 

and  Dittmar,     W.,     estimation     of 

potassium 422 

Machinery  for  classifying 172 

concentrating 187 

crushing    135 

for  grinding 146 

Maclaurin,  J.  S.,  influence  of  oxygen  on 
solution   of   gold    and   silver   in 

cyanide 102 

influence  of  strength  of  solution 105 

Macquer,  researches  on  Prussian  blue  .  4 
Mactear,  J.,  method  for  manufacture  of 

cyanide 131 

Magenau,  V.,  assay  of  rich  cupels    374 

zinc-box  precipitate 377 

Magnesium  cyanide,  properties  of.  ...  69 

Magnesium,  estimation  of    416 

in  water 472 

volumetric  estimation  of 416 

Makins,  G.  H.,  action  of  nitrous  acid  on 

gold 347 

Manganese,  cyanide  of   71 

Manganese  dioxide,  as  auxiliary  solvent  294 

as  flux 125,  270 

estimation  of,  available 418 

Manganese,  estimation  of    417 

in  solutions    448 

separation  of 416 

Manganicyanides    94 

use  of,  as  gold  solvents   104 

Mauganocyanides , 94 


INDEX 


511 


PAGE 

Manufacture  of  cyanide 127 

from  ammonia 130 

ammonium  compounds 130 

animal  matter 127 

atmospheric  nitrogen 128 

illuminating  gas    131 

thiocyanates 132 

trimethylamine    131 

raw  materials  for 127 

Marais  (see  Bettel) 
Margueritte  and   DeSourdeval,   manu- 
facture of  cyanide    129 

Margoshes,  B.  M.,  estimation  of  ferro- 

cyanide 435 

Marsden  crusher 135 

Marsh's  test  for  arsenic 403 

Mason,   W.  P.,  and   Bowman,  J.  W., 

losses  in  cupellation 344 

Materials    used  in  cyanide    manufac- 
ture   127 

used  in  cyanide  process,  analysis  of .  .  463 

Matte,  analysis  of 430 

treatment  of,  in  fusions  of  zinc-gold 

precipitate    271 

May     Consolidated    mine     (Johannes- 
burg),   crushing    with    cyanide 

solution 281 

Mechanical  difficulties  in  treatment  of 

crushed  ore    33 

handling  of     material     for     cyanide 

treatment 159 

haulage  of  tailings 163 

losses  of  zinc  in  precipitation 254 

Mein,   Capt.   G.  A.,   and  Butters,   C., 

automatic  pulp-distributor    .  . .  166 
Mercur  mine   (Utah),  coarse  crushing 

for  cyanide  treatment 171 

Mercur  (Utah),  zinc-dust  precipitation 

at 306 

Mercuric  chloride,  use  of,  as  auxiliary.  297 
Mercuric  cyanide,  analysis  of,  by  Gay- 

Lussac 7 

preparation  and  properties  of 81 

solvent  effect  of 17 

Mercury,  basic  cyanides  of 82 

cyanides  of  . 81 

double  cyanide  of,  and  potassium ...  82 

effect  of,  on  zinc  precipitation 120 

estimation  of 418 

feeding  into  mortar-boxes 181 

fulminate  of 98 

sickening  of 182 

use  of,  as  cathode 303 

use  of,  in  amalgamation 179 

Merrill,  C.  W.,  filter  press 221 

Merton  furnace 287 

Metallic  coatings  in  zinc  precipitation .  .  254 
compounds     of     complex     cyanogen 

radicals 84 


PAGE 

Metallic  compounds  of  cyanogen  with 

oxygen  or  similar  elements  ....  95 

cyanates 96 

Metallic  cyanides,  action  of  acids  on ...  64 

action  of  chlorine  on 63 

heat  on 63 

oxygen  on    63 

water  on 64 

complex 84 

constitution  of 63 

general  methods  of  formation 62 

general  properties  and  reactions ....  63 

simple 62 

Metallic    Extraction    Co.     (Colorado), 
acid    treatment    of    roasted    pre- 
cipitate    262 

Metallic  radicals  in  cyanide,  estimation 

of 459 

Metallics  in  assay  samples 372 

Metallic  sulphides,  action  of,  on  cyanide  1 13 

Metallurgical  tests 475 

Metals,   dissolved   in  cyanide  without 

oxygen 103 

electrochemical  order  of,  in  cyanide  18,  106 

estimation  of,  in  solid  cyanide 459 

in  solutions    447 

in  bullion 433 

Metric  weights  and  measures,  conver- 
sion of 498 

Mexico,  crushing  with  cyanide  in 285 

electrolytic  precipitation  in    301 

slime  treatment  by  aeration  in 210 

Meyer  and  Charlton  Gold  Mining  Co., 

details  of  cyanide  treatment ....  283 
Mill-product,  handling  of,  for  cyanide 

treatment 165 

Mill,  Ball 152 

Bryan    150 

Chilian    149 

Flint 37 

Huntington    150 

Stamp 137 

Tube 37,154 

Miller  and  Fulton,  assay  of  cupels 374 

assay  of  rich  slags 373 

in  cupellation 344 

in   scorification 353 

Miller,  Hall  and  Falk,  assay  of  pyritic 

ore  with  niter 363 

Millieme  system  of  reporting  assays .  . .  386 

Milling  practice  with  rolls 146 

with    stamps 144 

with  tube  mills 155 

Minas     Prietas,     Mexico,     electrolytic 

precipitation  at 301 

experiments  on  hot  solutions  at 239 

Mine  sampling    321 

Minerals,  electrochemical  order  of,  in 

cyanide  solutions    106 


512 


INDEX 


PAGE 

Mitchell,  assay  of  pyritic  ore 361 

Mixing  of  precipitate  and  fluxes    ....  267 

of  assay  samples 328 

Modern  systems  of  concentration 188 

of    metallurgy 193 

Modifications  of  cyanide  process 278 

Moldenhauer,  C.,  use  of  ferricyanide  as 

auxiliary  solvent 294 

Moir,  Dr.  J.,  colorimetric  estimation  of 

gold 445 

Moisture  in  assay  samples 329 

in  coal,  estimation  of 465 

in  cyanide,  estimation  of 461 

in  ores,  estimation  of    427 

in  samples  for  analysis 396 

Molloy  process      304 

Montejus 210,  219 

Moore  filter 222 

details  of  working    223 

Moore,  T.,  estimation  of  nickel 419 

Morris,    C.   J.,   details    of    zinc    clean- 
up    262 

Mortar-box,  construction  of 142 

Muffle  furnaces  .  .  : 340 

charging  cupels  into    341 

Muhlenberger,   alleged   anticipation   of 

cyanide  process 23 

Muntz  metal,  use  of,  for  amalgamated 

plates  in  battery 181 

Myall's     United      mines      (Australia), 

treatment  of  zinc  precipitate  at .  262 

Natural  settlement  of  sands  and  slimes .  159 
Nevada,  crushing  with  cyanide  solution 

in 284 

cyanide  practice  in    225,  284 

slime  treatment  in 225 

New    Goch    Gold    Mining    Co.,    sand 

sampling 325 

Nicholas     and     Nicols,     treatment     of 

cupriferous  ores 310 

Nickel,  cyanide  of 71 

separation  and  estimation  of 419 

Niter,  assaying  with    363 

use  of,  in  assaying  ores  of  antimony .  .  366 
use  of,   in  •  fluxing  zinc-gold   precipi- 
tate     125, 266 

use  of,  in  roasting  zinc  precipitate    .  .  264 

Nitrates,  estimation  of,  in  solutions.  .  .  449 

Nitric  acid,  action  of,  on  gold 385 

use  of,  in  assaying 345,  384 

use  of,  in  treatment  of  zinc-gold  pre- 
cipitate   123,  262 

Nitrites,   estimation   of 449 

Nitrogen,  atmospheric,  manufacture  of 

cyanide  from    128 

Nitrogenous    matter    (organic),    manu- 

acture  of  cyanide  from 127 

Nitroprussides 93 


PAGE 

Nitroprussides,  characteristic    colors  of  94 

general  properties  and  reactions ....  94 
use  of,   in  detecting  and  estimating 

sulphides  in  solution 450 

Nitrous  acid,  action  of,  on  gold  in  part- 
ing    347 

Non-metals,  action  of  hydrocyanic  acid 

on 54 

cyanogen  compounds  of 47,  56 

estimation  of,  in  cyanide 456 

solutions 448 

Norseman    mine    (W.    Australia),   Ball 

mill,  products  at 154 

Oil,  concentration  by    191 

effect  of,  in  amalgamation 183 

Old  tailings,  preparation  of,  for  cyanid- 

ing 159 

Ore,  assay  of 333-371 

analysis  of 395-429 

concentration  of 185,  192 

crushing  of 135,  143,  281 

grinding  of 146 

sampling  in  mine 321 

treatment  of  cupriferous 112,  301 

telluride    286,  297 

Organic'  carbon,  estimation  of 473 

Organic  matter,  estimation  of,  in  solu- 
tions          452 

in  water 473 

Outline  of  ore  analysis 396 

of  operations  in  cyanide  process ....        33 
Oxalates,  estimation  of,  in  solutions.  .  .      452 
Oxidation,  effect  of,  in  cyanide  treat- 
ment  11,  18,  102,  109,  293 

of  metals  in  molten  bullion 125 

Oxides,  action  of,  on  cyanide 66 

on  hydrocyanic  acid 55 

Oxidizers,  action  of,  on  gold  in  cyanide 

solution 18 

in  conjunction  with  cyanide.  .  .  18,  103,  293 
Oxygen,  Dixon's  experiments  on,  in  con- 
junction with  cyanide 18 

Eisner's  experiments  on    11 

estimation  of,  in  ores    419 

Faraday's  experiments  on    13 

heat  of  combustion  of  metals  with       125 

influence  of,  on  cyanide 63,  109 

on  solubility  of  metals  in  cyanide 

11,  13,  18,  102,293 

Maclaurin's  experiments  on 102 

necessity  of,  in  cyanide  process....      102 
refining  zinc-precipitate  by    43,  276 

Pachuca  agitation  tanks 210 

Pan  amalgamation 180 

test  to  imitate 489 

Paracyanogen,   preparation  and    prop- 
erties ..  51 


INDEX 


513 


PAGE 

Parting  assay  beads 345,  384 

bullion  assays    384 

in  crucibles    345 

in  flasks    346,  384 

platinum  apparatus  for 384 

precautions  in 385 

testing  acid  for  use  in    346 

Pearce,  Dr.  R.,  estimation  of  arsenic .  .  .  403 

Pelatan-Clerici  process    304 

Pelouze,  J.-,  production  of  formates  from 

cyanides    • 9 

Pelouze's  green 92 

Penfield,  estimation  of  fluorine 413 

Percolation,  conditions  for  effective  .  .  200 

definition  of 195 

process    35,  195 

tests 493 

upward 204- 

Percussion  tables    188 

Percy,  J.,  assay  of  cupels 374 

assay  of  cupriferous  ores    368 

assay  of  slags    373 

proportions  of  lead  in  cupellation  of 

copper  ores    369 

solubility  of  silver  in   cyanide   solu- 
tions      20 

Perferricyanides 93 

Permanganate,  use  of,  as  auxiliary  dis- 
solving agent 294 

Peroxide  of  hydrogen,  formation  of,  in 

reaction  of  cyanide  on  gold 102 

Peroxide  of  lead,  coating  anodes  with .  .  300 
Phosphoric  acid,  in  ores,  separation  and 

estimation  of 420 

Phosphorus  in  coal,  estimation  of 467 

Picard,  H.  K.,  mixer  for  zinc-dust 308 

zinc-dust  in  connection  with  bromo- 

cyanide  process 306 

Piping  for  conveying  solutions 237 

Platinum  parting  apparatus 384 

Plates,  amalgamated  copper,  in  battery  180 

filter 222 

Muntz  metal 181 

Poisoning  with  arseniureted  hydrogen  .  261 

with  cyanide  and  hydrocyanic  acid .  .  55 

with  cyanide,  antidotes  for 55 

Polymer  of  cyanifc  acid 98 

of  cyanogen 5-1 

of  cyanogen  bromide 59 

of  cyanogen  chloride 57 

of  hydrocyanic  acid 55 

Porrett,  R.,  discovery  of  sulphocyanides  7 

electrolysis  of  ferrocyanides 7 

Possoz  and  Boissiere,   manufacture  of 

cyanide  128 

Potassium  aurocyanide 73 

copper  cyanides    79 

cyanate 97 

Potassium  cyanide,  action  of  alkalis  on  67 


PAGE 

Potassium  cyanide,  action    of    metals 

on 67 

analysis  of  commercial 455 

manufacture  of 9,  127 

preparation  of 65 

properties  and  reactions  of    66 

synthesis  of 65 

use  of  in  amalgamation 14,  21,  183 

Potassium,  estimation  of,  in  cyanide.  .  .  460 

in  ores 421 

in  water 472 

ferricyanide    90 

use  of,  as  auxiliary  dissolving  agent  294 
ferrocyanide  preparation,   properties 

and  reactions 86 

-ferrous  ferricyanide 93 

-silver  cyanide 75 

thiocyanate    100 

-zinc  cyanide 70 

-zinc  ferrocyanide 90 

Power  required  for  Ball  mills 154 

for  Huntington  mills 151 

for  Rock-breakers 136 

for  Tube  mills 158 

Precipitate,  white,  composition  of....  119 

Precipitating  surface,  influence  of 251 

Precipitation,  alternative  methods  of .  .  39 

by  aluminium 122 

by  charcoal    122,  308 

by  cuprous  salts 123,  309 

by  zinc-dust    40,  124,  306 

by  zinc  shavings 28,  38,  117,  241 

chemistry  of    117 

conditions  of 38,  117,  248 

effect  of  copper  in 120 

in  circular  vats 245 

influence  of  various  factors  on  ....  38 
of  copper  by  acids  in   cyanide  solu- 
tion    312 

on  silver  and  copper ,. . .  19 

reactions  in    117 

Precious    metals,     estimation    of,      in 

bullion 431 

solubility  of,  in  cyanide 4,  20,  105,  454 

Preparation  of  charges  for  leaching ....  200 

of  ore  for  direct  cyaniding 170 

Preparatory  treatment  of  ore  for  cyanid- 
ing    133 

Presses  (see  Filter-Presses) 

Pressure  filters    216 

Protective  alkali,  estimation  of 439 

Proust,  investigations  on  prussiates.  .  .  6 

obtains  cyanogen 7 

Prussian  blue,  discovery  of 3 

manufacture  of 3 

preparation,     properties,    and    reac- 
tions    89 

researches  on 4,  5 

soluble    .  93 


514 


INDEX 


PAGE 

Prussian  green 92 

Prussiates,  early  investigations  on  ...  6 
Prussic  acid  (see  also  Hydrocyanic  Acid) 

composition    5 

discovery  of 4 

early  use  of 3 

in  natural  products 6 

Ittner's  researches  on    7 

Scheele's  researches  on 4 

Pulp  distributor 166 

Pumps,  agitation  by  centrigufal 210 

centrifugal    237 

for  transferring  solution 237 

Frenier  sand 169 

Push  conveyor    287 

Pyrites,  action  of,  on  cyanide 110 

effect  of,  in  amalgamation 182 

Pyritic  concentrates,  assay  of 361 

Pyritic  ore,  assay  of 359 

Quantities  and  strength  of  solution  in 

sand  treatment 35,  203 

Quartering  assay  samples 317 

Quartz  ores,   assay  of 333,  355 

Rae,  J.  H.,  patent 15 

Rand,  E.  T.,  continuous  slime  settle- 
ment    214 

Rand,  battery  practice 144 

crushing  with  cyanide  solution  on..  282 

fluxing  of  zinc-gold  precipitate 286 

flux  for  chlorination  tailings 358 

pyritic  concentrates 361 

siliceous  ore  and  tailings 356 

mine  sampling  on 321 

sand  collecting  on 166 

scorification  assay  on 254 

slime  treatment  on 212,  221 

Rate  of  flow  in  zinc-boxes 250 

Redjang  Lebong  mine  (Sumatra) 

clarifying  solutions  by  filter-press  at.  236 

composition  of  bullion  at 263 

flux  for  siliceous  ore  at 356 

grading   tests   on   sands   before    and 

after  cyaniding  at    144 

selenium  in  zinc-precipitate  at 253 

tilting  furnace  at   269 

Reducing  agents  in  assaying 334 

power  of  solutions,  estimation  of    ...  453 

Reed,  S.  A.,  theory  of  sampling 320 

Refining  of  bullion 275 

with  oxygen 43,  276 

Refractory  materials,  assay  of  certain.  .  371 

ores,  cyanide  treatment  of 286 

Regeneration  of   cyanide   solutions  by 

acids    115 

Remelting  of  cyanide  bullion    270 

Reporting  assay  results 348 

Reprecipitation  of  gold  and  silver  during 

the  dissolving  process 115 


PAGE 

Residues,  discharging  of  sand 206 

discharging  slime    .'  .214,  220 

from  zinc  retorts,  assay  of    377 

Reverberatory  furnace  for  roasting  zinc- 
gold  precipitate 268 

Revolving  cylindrical  furnaces    288 

Richmond,    C.    P.,    electrolytic    treat- 
ment of  gold-copper  ores 121,  301 

Ridgway  filter 230 

practice  with,  at  Great  Boulder,  W. 

Australia 232 

Riecken  process    304 

Rittinger,  pointed  boxes  for  classifying  172 

Roasting,   assay  by 359 

for  cyanide  treatment 114,  171,  286 

furnaces    286 

Argall 288 

Edwards   286 

Merton 287 

zinc  precipitate 42,  124,  264,  268 

Robinson     Deep     Gold     Mining     Co., 

stamp  battery  practice  at 143 

Tube  mill,  products  at 157 

Robinson  Gold  Mining  Co.  (Transvaal), 

early  slime  treatment  plant  at ..  221 

establishment  of  cyanide  process  at .  .  30 

flux  for  low-grade  ore  at 356 

Rock-breakers 135 

jaw 135 

gyratory 136 

Rodgers,    F.    and   E.,    manufacture   of 

cyanide 9 

Rolls,  crushing  with,  at  Cripple  Creek .  .  154 

Argall    148 

Hadfield    147 

modern  practice  with 146 

Rose,     Dr.     T.     Kirke,     amalgamated 

copper  plates  as  cathodes    ....  303 

analysis  of  bullion  from  zinc  process .  275 

assay  of  cupels 374 

early  practice  of  amalgamation 14 

efficiency  of  rock-breakers 136 

falling  bodies  in  water    173 

flux  for  siliceous  ores    355 

inside  amalgamation    180 

refining  zinc  precipitate  and  bullion 

with  air  or  oxygen 43,  125 

remarks  on  scorification 353 

roasting  of  ores 171 

Roskelley,  T.,  stamp  battery  practice.  143 
Rowland  process  of  cyanide  manufac- 
ture   131 

Sal-ammoniac,  use  of,  in  amalgamation .  183 
Salisbury  battery   (Johannesburg),   in- 
troduction of  cyanide  process  at .  30 

Sample,  definition  of 317 

Samplers,  automatic    325 

Vezin  .  .  .318 


INDEX 


515 


Samples,  bullion 378,  430 

containing  dissolved  values    332 

drying 330 

location  of,  in  tanks 326 

mixing,  dividing  and  quartering  .  . .  328 

moisture 329 

precautions  in  preparing 323 

reduction  of 330 

residue 328 

taken  in  discharging  sand  tanks    . .  328 

Sampling 317 

bullion 430 

coal 465 

conditions  for  accurate 324 

cyanide  455 

implements    323 

large  heaps 317 

lime 463 

mine  ore 321 

ores   317 

rod 326 

objections  to 326 

sand  and  similar  material 324 

difficulties  in 324 

slime    332 

theory  of    320 

trucks    325 

water 468 

Sand  charges,  calculating 477 

determining  density  of    477 

collection  of 34 

definition  of 33 

natural  settlement  of,  in  pits 159 

pumps 169 

sampling 325 

treatment  by  percolation 35,  195 

Sander,K.,assay  of  carbonaceous  matter  377 

Sanders,  J.  F.,  patent    .r 21 

Sands  and  slimes 33 

San  Sebastian  mine    (Salvador),  elec- 
trolytic process  at    121,  301 

Santa    Francisca    mine      (Nicaragua), 

Gilmour- Young  process  at .  .    .  .  306 
Scheele,  observations  on  cyanides  of  gold 


and  silver 


4 

researches  on  prussic  acid  4 

Scorification  assay  349,  351 

theory  of  352 

difficulties  in 352 

in  fusion  furnaces 353 

lead  required  in  351 

of  bullion  assays 382 

of  large  lead  buttons 353 

of  material  containing  copper 350 

of  rich  silver  ore 350 

of  zinc  box  precipitate 351 

precautions  in 353 

theory  of 352 

Scorifiers 349 


PAGE 

Scorifier  tongs 352 

Screen  analysis 435 

Callow iQi 

Screening  tests    435 

Scrymgeour,    use   of   cupriferous   solu- 
tions as  preliminary  solvents.  .  .  311 
Selective  action  of  dilute  solutions ...  26,  107 

Selenium,  action  of  cyanide  on    66 

detection  of 423 

estimation  of,  in  bullion 434 

in  ores 422 

in  solutions    450 

in  zinc  precipitate    123,  253 

removal  of,  in  smelting 269 

Separation  of  coarse  zinc  (shorts) 258 

of  dissolved  values  in  slime  treatment  36 

of  gold  and  silver  by  cadmium 431 

of  sands  and  slimes. 172 

tests  (hydraulic)   485 

Serullas,  discovery  of  cyanogen  bromide  9 

Settlement,  agents  used  for 177 

of  slimes 176,  212 

of  zinc  precipitate    259 

tanks,  conical    176 

for  slime 176,  214 

Settling  pits 165 

Shaking  amalgamated  plates 282 

Sharwood,  W.  J.,  reaction  of  cyanide  on 

zinc  oxide 118 

zinc-dust  practice 307 

"Shorts"    260 

treatment  of    263 

Siemens,  Dr.  W.,  invention  of  electroly- 
tic process   40 

Siemens-Halske  process 40,  121,  298 

advantages  and  disadvantages  of  .40,299 

Sifting  samples  for  assay 324 

samples  for  analysis 395 

Silica,  estimation  of,  in  ores 423 

in  water 472 

use  of  as  flux  for  zinc  precipitate ....  266 

in  assaying 334 

Silicates,  estimation  of,  in  cyanide 459 

Siliceous  material,  analysis  of 395 

ores,  assay  of 333,  355 

Silver  cyanate 97 

Silver  cyanide 74 

action  of  acids  and  sulphur  on 75 

preparation,  properties,  and  reactions  74 

Silver,  Deniges  method  of  estimating  433 

double  cyanide  of  potassium  and  . .  75 

double  cyanides  of 75,  76 

estimation  in  bullion 432 

solutions 446 

ferrocyanide  of   87 

ferricyanide  of 93 

Gay-Lussac's  method  of  estimating  .  389 

Silver,  separation  from  gold  in  alloys  43 J. 

solubility  in  cyanide    20 


516 


INDEX 


PAGE 

Silver,    Volhard's  method   of  estimat- 
ing   390,  433 

volumetric  assays  of 389 

Simon,  Dr.  F.,  Ball  mill  practice 154 

Simpson,  D.,  automatic  sand  sampler.  325 

sampling  sand  in  tanks    327 

Simpson,    E.    W.,    details    of    furnace 

practice 287 

Simpson,  J.  W.,  patent 22 

Size  of  stamp-mill   product,   condition 

regulating 141 

Sizes  of  samples  allowable  at  different 

stages  of  crushing    319,  331 

in  relation  to  grade  of  ore    320 

Sizing  tests,  method     of     making     in 

laboratory 485 

on  Ball  mill  product 154 

on  Roll  product 147 

on  Tube  mill  product 157 

Skey,  W.,  conditions  of  amalgamation.  17 
electromotive     order     of     metals    in 

cyanide   18 

relative     solubility     of     metals     in 

cyanide 17 

Slag,  assay  of,  by  scorification 352 

assay  of,  from  zinc  precipitate 373 

from  fusions  of  zinc  precipitate ....  270 
treatment     of,     by     litharge     smelt- 
ing   42,125,272 

Slime,  aeration  of 210 

agitation  treatment  of 36,  209 

coagulation  of 177 

collection  of 35 

decantation  treatment  of 36,  212 

deep  tanks  for  settling   214 

definition  of 34 

deposition  of,  by  natural  settlement  160 

determining  density  of    478 

effect  of,  in  sand  treatment    160 

first  plant  in  S.  Africa  for  treating.  .  221 

pulp  densities,  calculation  of 479 

sampling 332 

separation  of 172 

settlement  of 176,  212 

solutions,  requisite  alkalinity  of   ...  257 

use  of  lime  in  settling    177 

Smelting,  chemistry  of    124 

of  bullion 270 

of  zinc  precipitate 41,  124,  241 

of  zinc  precipitate  with  litharge  42,  125,  272 

Smith,  E.  A.,  assay  of  antimonial  ores.  .  366 

arsenical  ores 366 

basic  ores 358 

cupriferous  ores 368 

pyritic  ores    362 

slags 373 

telluride  ores  370 

assay  with  niter 363 

oxidizing  effect  of  niter    364 


PAGE 

Smith,  E.  A.,  volumetric  assay  of  silver  391 
Smith,   Lawrence,  estimation  of  alkali 

metals  in  ores 397 

Smith,  R.,  solubility  of  silver  in  cyanide  20 

Soda,  caustic,  use  of  in  amalgamation.  .  184 

carbonate  (see  Sodium  Carbonate) 

Sodium  amalgam,  precipitation  by.  ...  122 

use  of  in  amalgamation    184 

argentocyanide    76 

bisulphate,  use  of  in  clean-up  .  .  .  123,  262 
carbonate,    use  of,    for   precipitating 

foul  solutions 250 

chloride,  use  of,  in  conjunction  with 

cyanide 21 

cyanide,  formation  and  preparation  of  67 

properties  and  reactions 68 

estimation  of,  in  cyanide   459 

in  ores 421 

in  water 472 

ferrocyanide 89 

gold  cyanides 73 

metallic,  use   of,  in   manufacture   of 

cyanide   128,  130 

nitroprusside    94 

use  of  as  indicator 450 

peroxide,  use  of,  as  auxiliary  solvent  293 

potassium    argentocyanide 76 

Solids,   dissolved,  estimation  of,   in  cy- 
anide solutions    453 

in  water 471 

suspended,  estimation  of,  in  solutions  453 

in  water 471 

Solubility  of  gold  and  silver  in  cyanide 

4,  6,  20,  105 

Elkington's  observations  on 10 

effect  of  alkali  on    109 

effect  of  base  metal  compounds  on  110 

effect  of  carbonic  acid  on    109 

copper  on Ill 

external  influences  on 108 

other  substances  on 106 

oxygen  on    109 

strength  of  solution  on 105,  107 

temperature  on 106 

Hagen's  observations  on 6 

MacArthur's  observations  on    24 

Maclaurin's  observations  on    102 

Scheele's  observations  on 4 

Wright's  observations  on 10 

Solution,  absorption  of,  by  wooden 

vats 199 

analysis  of 437 

and     electrolytic     precipitation     in 

same  vessel    304 

crushing  with  cyanide 382 

Solvent  activity,  estimation  of 454 

South  Africa  (see  Rand,  etc.) 

South  Dakota  (see  Black  Hills) 

Specific  gravity  determinations 478 


INDEX 


517 


PAGE 

Specific  gravity  of  slime  pulp,  calcula- 
tion of 479 

Spitzkasten 36,  172 

Spitzliitten 34,  172 

conditions  of  working 175 

conical 175 

details  of  construction 174 

Stamp  battery  practice 143 

Stamps,  crushing  with    137 

mode  of  action 138 

Standard  cyanide  test 490 

flux  for  siliceous  ore    334 

Stines,    N.    S.,   estimation   of    gold   in 

solutions 444 

Stockhausen,  F.,  composition  of  bul- 
lion bars 275 

sampling  of  bullion    378 

Storage  tanks,  dimensions  of 235 

for  solutions 235 

Strength  of   solution,  •  influence   of,    in 

dissolving  gold  and  silver 105 

in  sand  treatment    202 

in  slime  treatment 209 

Strong  solution  treatment    202 

Strontium  cyanide 69 

estimation  of 404 

Suction  filters,  early  use  of 221 

Sulman,  H.  L.,  bromocyanide  reactions  58 

double  cyanides  of  copper 79 

tilting  furnace  for  zinc  precipitate  .  269 
Sulman  and  Picard,  zinc-dust  precipi- 
tation     40,306 

Sulman-Teed,  bromocyanide  process .  .  295 

Sulphates,  effect  of,  in  acid  treatment.  263 

estimation  of,  in  solutions    449 

water 472 

insoluble,  deposited  in  zinc-boxes  .  .  253 

Sulphides,    colorimetric    estimation    of  450   . 

detection  of ". 450 

estimation  of,  in  cyanide 459 

in  solutions    449 

metallic,  action  of,  on  cyanide 16,  113 

Sulphocyanides  (see  Thiocyanates) 

Sulphotelluride  ores,  treatment  of ....  294 

Sulphur,  estimation  of,  in  coal    466 

in  metals    S- 434 

in  ores 425 

in  solution 450 

occurrence  of,  in  zinc  precipitate. .  . .  253 

separation  of,  in  ores    425 

Sulphuric  acid,  use  of,  in  treatment  of 

cupriferous  ores 310 

use    of,    in    treating    zinc    precipi- 
tate  41,123,261 

Sulphurous  acid,  use  of,  in  preliminary 

treatment  of  cupriferous  ores..  311 

Sumps 235 

Surcharge  of  bullion  assays 387 

Surrogat,  cyankalium    129 


PAGE 

Suspended  matter,  estimation  of  ..453,471 

influence  of,  in  zinc  precipitation  ....  248 
Sutton,  F.  (volumetric  analysis) 

estimation  of  antimony 401 

chlorine 408 

copper 411 

ferricyanides 442 

hardness  of  water 471 

lime 464 

nitrates 449 

organic  matter  in  water 473 

urea 452 

Synthesis  of  cyanogen 48 

of  hydrocyanic  acid 52,  54 

of  potassium  cyanide 62,  65 

of  urea   8 

System  of  crushing  with  cyanide    at 

Black  Hills 284 

on  Rand 282 

System  of  continuous  slime  settlement  214 
System  of  treatment  by  concentration 

followed  by  cyanide 192 

Tables,  concentrating    187 

endless  belt    191 

percussion 188 

Wilfley    188 

Tables  for  converting  metric   weights 

and  measures 498 

of  atomic  weights 499 

Tailings,  accumulated,  treatment  of.  .  159 

current,  handling  of 165 

double  treatment  of 205 

pumps 169 

transfer  of-   163 

treatment  of  unsized 161 

wheels 167 

Tanks,     absorption     of,     solution     by 

wooden 199 

calculating  contents  of    477 

clarifying    236 

deep,  for  slime  settlement 214 

filling,  by  hose 165 

intermediate  filling 166 

iron    197 

leaching 195 

remedies  for  leaks  in 198 

square   197 

steel 197 

wooden 197 

Tatlock,  estimation  of  potassium 421 

Tavener,  P.  S.,  automatic  lime  feeder ...  178 
conditions  of  crushing  for  amalgama- 
tion     145 

process    for    treating    zinc    precipi- 
tate    42,125,272 

smelting    precipitate    with    litharge 

42,  125,  272 

vats  for  zinc  precipitation 245 


518 


INDEX 


PAGE 

Telluride  ores,  assay  of    369 

treatment  by  bromocyanide 297 

treatment  by  roasting 286 

Tellurium,  action  of,  on  cyanide 114 

assay  of  ores  containing 369 

detection  of 426 

estimation  of,  in  ores    423 

in  solution 450 

in  zinc  precipitate    123 

Temperature,  effect  of,  in  cupellation  342 

on  extraction 239 

"Test"  for  cupellation  of  lead  bullion  273 

Tests,  amalgamation 488 

concentration 487 

cyanide  extraction    490 

for  acidity  of  ores 483 

for  regulating  zinc-box  work 256 

grading 485 

hydraulic  separation    485 

used  in  routine  of  plant 438 

Thames  Gold  Field  (New  Zealand),  use 

of  cyanide  in  amalgamation   ....  17 
Theft   of   zinc   precipitate,   precautions 

against    256 

Theory  of  sampling 320 

of  scorification 352 

of  slime  treatment  by  decantation  212 

Thiocyanates,  discovery  of 7 

estimation  of 442 

general  modes  of  formation 99 

manufacture  of  cyanide  from    132 

properties  and  reactions   99 

use  as  indicator  for  iron    414 

Thiosulphates,  estimation  of 450 

occurrence  in  cyanide 459 

Thomas,  J.  E.,  and  Williams,  G.,  use 
of  sodium  bisulphate  in  treat- 
ment of  zinc-gold  precipitate .  .  .  262 

Tin,  estimation  of    426 

Titanium,  estimation  of 427 

Tonopah  Mining  Co.  (Nevada),  cyanide 

practice 284 

Total  alkali,  estimation  of 451 

Total  cyanide,  estimation  of 440 

cyanogen,  estimation  of    440 

dissolved  solids,  estimation  of 453 

sulphur,  estimation  of 450 

Transfer  of  material    163,  167 

by  conveyors 167 

by  tailings  wheels 167 

Traveling  belt  niters   226 

belts 167 

Traversing  type  of  vacuum  filter  ....  226 
Truscott,  S.  H.  and  Yates,  A.,  clarify- 
ing solutions  by  filter  press  ....  236 

Tube  mills 37,  154 

conditions  for  maximum  efficiency  of  155 

Davidsen    155 

liners  for  .  .                                        .  .  154,  158 


Tube  mills,  power  required  for. 

use  of  banket  in 

Turnbull's  blue  

Types  of  roasting  furnaces  .  .  . 

vacuum  filters  .  . 


PAGE 

158 
156 
92 
286 
221 


Union  mine  (Amador   Co.,  California), 

use  of  cyanide  in  battery  at.  ...  16 

United  States,  cyanide  practice  in 284 

Upward  percolation   204 

Urea,  estimation  of,  in  solutions 452 

synthesis  of 8 

Useful  formula 496 

Vacuum  filters 37,  221 

filtration  of  sands 222 

slimes    222 

Valves,    arrangement    of,    on    solution 

pipes    237 

suction,  for  aerating  pulp    210 

Vats  (see  also  Tanks) 

conical 211,284 

steel 197 

wooden 197 

Vauquelin,  discovery  of  cyanic  acid    ...  8 

occurrence  of  prussic  acid  in  nature.  6 

Vegetable  matter  in  tailings 161 

Vezin  sampler  319 

Victor,  E.,  reactions  of  cyanates 98 

Victoria  (Australia),  charcoal  precipita- 
tion in 308 

Virginia  City  (Nevada),  slime  filtration 

at 225 

treatment  of  cupriferous  ore  at 310 

Virgoe,    W.    H.,    double    cyanides    of 

copper 79 

losses  of  zinc  in  precipitation 254 

mercury  in  zinc  precipitate 251 

precipitation  of  zinc  and  lime  in  the 

extractor  boxes 256 

Volatile  matter,  in  coal,  estimation  of  .  465 

Volhard,  estimation  of  silver 390,  433 

Volumes  of  conical  vessels,  calculation  of  477 

tanks 477 

Volumetric  estimation  of  cyanide 438 

earliest  notice  of 11 

of  silver    389 

Waihi  Gold  Mining  Co.  (New  Zealand), 

air-lift  slime  agitator  at 211 

crush  filter  at 226 

gradings  of  Tube  mill,  products  at.  .  157 

Tube  mill  liners  at 158 

Waller,  H.  T.,  estimation  of  aluminium  399 

iron  in  slags    414 

zinc  in  slags    429 

Washing,  alkali    201 

cakes  in  filter  press 220 

final  water  .  .                                           .  204 


INDEX 


519 


PAGE 

Washing,  preliminary  water 201 

Water,  analysis  of 467 

estimation  of,  in  ores    427 

hardness  of    471 

sampling .  467 

use  of,  in  cyanide  treatment 201 

Weak  solution  in  treating  sands 203 

Weighing  assays,  charge  of  ore 336 

bullion   assays 379,  383 

fine  metal 344 

gold  cornets 386 

parted  gold    347 

weights  and  measures 498 

assay 386 

West  Africa,  treatment  of  zinc  precipi- 
tate in 267 

West  Australia,  Ball  mill   practice  in.  .  154 

bromocyanide  practice  in 297 

Ridgway  filter  in 232 

roasting  for  cyanide  treatment  in ...  286 
Whitby,  A.,  analysis  of  "white  precipi- 
tate"     119 

analysis  of  acid-treated  and  roasted 

zinc-precipitate    363 

estimation  of  gold  in  solutions 443 

White,  F.,  treatment  of  tailings 205 

White  precipitate  in  zinc-boxes 118,  252 

analysis  of 430 

composition  of 119 

conditions  and  formation 118 

Whitehead,  C.,  assay  of  cupriferous  ores  368 

Wilde,  P.  de,  precipitation  of  gold  from  " 
cyanide    solutions    by    cuprous 

salts 123,  309 

Wilfley  concentrating  table    188 

Williams,    Gerard,   W.,   bromocyanide 

practice 296 

estimation  of  carbonates 448 

lime   464 

Williams,  S.  H.,  absorption  of  solution 

by  wood 1" 

Witwatersrand  (see  Rand) 
Woltereck,     H.     C.,     manufacture     of 

cyanide 131 

Wood,    T.    W.,    surcharge    of    bullion 

assays    387 

Wooden  vats,  absorption  of  solution  by  199 

construction  of    197 

Woodward,   manufacture    of    Prussian 

blue  •  3 

Wohler,    F.,    composition    of    azulmic 

acid 5(> 

synthesis  of  urea    8 

Worcester  mine   (Transvaal),  Siemens- 

Halske,  process  introduced  at  .  298 
Wright,  Dr.  A.,  solubility  of  gold  and 

silver  in  cyanide 10 

Wurtz,  Prof.  H.,  use  of  cyanide  in  amal-  - 

gamation 14 


PAGE 

Yates,  A.  and  Truscott,  S.  H.,  clarify- 
ing solutions  by  filter  press  . . .     236 

Zinc,  accumulation  of,  in  solutions    39 

ammonium  cyanide 71 

argentocyanide    76 

assay  of  ores  containing 365 

Zinc-boxes    38,    243 

charging  of 247 

clean-up  of 258 

construction  of    243 

deposits  in 118,  252 

dimensions  of    243 

empty  compartments  in 247 

practice 247 

rate  of  flow  in    250 

trays  for 243 

Zinc,  consumption  of 254 

-copper  couple 251 

Zinc  cyanide    69 

action  of  heat  on 70 

preparation  of 69 

properties  and  reactions 70 

Zinc,  double  cyanides  of    70 

double  ferrocyanides  of 90 

Zinc-dust    40,  124,  306 

advantages  of  precipitating  with    .  .       40 

at  Black  Hills 221 

at  Deloro,  Canada 306 

clean-up    124 

details  of  working  with    306 

difficulties  in  precipitating  with 308 

mixer  for    308 

recovery  of,  in  smelting* 269 

Zinc,  estimation  of 428 

in  solutions    447 

ferrocyanide 89 

-gold  precipitate  (see  Zinc  Precipitate) 

-lead  couple 38,  246 

-mercury  couple   251 

ores,  assay  on 365 

oxide,  solubility  in  cyanide 118 

-potassium  cyanide 70 

Zinc  precipitate 

acid  treatment  of 41, 123,  262 

arsenic  in 123 

assay  of    376 

composition  of 41 

fluxes  for    124,  266 

fluxing  with  niter 125,  266 

ingredients  occurring  in    121 

roasting 264 

roasting  with  niter 264 

treatment  of,  with  bisulphate 123 

with  hydrochloric  acid    262 

Zinc  precipitation 28,  117,  241,  306 

circular  vats  for 245 

conditions  which  influence 248 

details  of    .  ..117,241 


520  INDEX 

PAGE  *AOP, 

Zinc  precipitation,  difficulties  in 252        Zinc,  Simpson's  process  of 22 

discovery  of 29             separation  of 428 

hydrogen  evolved  in    252  shavings,  cutting  and  preparing  ...  246 

influence  of  iron  screens  in 255  first     use      of     for     precipitating 

MacArthur-Forrest,  process  of 28                    cyanide  solutions    29 

outline  of 38           slimes    241 


VD  07556' 


M127G43 


cofo  3 


THE  UNIVERSITY  OF  CALIFORNIA  LI 


